fix(qbittorrent): stop mislabeling gateway/URL errors as auth failures

The credential tester always reported "Authentication failed — qBittorrent
rejected the credentials" for the qBittorrent service, even when credentials
were correct. test_connection classified any RuntimeError whose message
contained "login failed" as an auth failure — and the gateway-timeout error
(502/503/504 from the reverse proxy) and the wrong-URL diagnostic both started
with "qBittorrent login failed:", so a proxy timeout was reported as a
credentials rejection. That sent users down the wrong path (re-entering correct
passwords to fix a 504).

- QbittorrentClient._login: gateway and URL/routing errors no longer contain
  "login failed"; only a genuine "Fails." body carries the
  "invalid username or password" signal.
- integrations/qbittorrent.test_connection: key the auth message off
  "invalid username or password" specifically; all other login errors flow
  through translate_connection_error so the real reason (proxy timeout, wrong
  URL, empty body) is surfaced.

After this, a failing test reports the actual cause (e.g. "qBittorrent is
unreachable: reverse proxy returned HTTP 504 ...") instead of accusing the
credentials. New regression test asserts a gateway error is NOT reported as
"Authentication failed". 386/386 backend tests pass; ruff clean.

backend/src/media_library_viewer_api/clients/.pi-map.md

@@ -4,7 +4,7 @@ dir: backend/src/media_library_viewer_api/clients
 index: backend/src/media_library_viewer_api/clients/.pi-map.index.md
 
 ## role
-Provides external service integration clients (API wrappers and command executors) for media servers, identity providers, torrent clients, and remote/local filesystems.
+Provides external service integration clients (API wrappers and remote/local command executors) for media library data aggregation and system monitoring.
 ## files
 - __init__.py | Swaps the position of two tmux panes within a window or between windows | dep: tmux, sh
 - authentik.py | API client wrapper for Authentik directory service providing paginated user browsing and search via REST API. | exp: class:AuthentikClient, method:__init__(self, base_url: str, api_token: str, timeout), call:base_url.rstrip, call:self.base_url.endswith, call:http_timeout, call:requests.Session, call:self.session.headers.update, raise:ValueError, method:get(self, path: str, **params: Any) → Any, call:params.items, call:logger.debug, call:sorted, call:clean_params.keys, call:self.session.get, call:response.raise_for_status, call:logger.warning, call:response.json, raise:requests.HTTPError, method:users(self, search, page, page_size) → dict[str, Any], call:self.get, call:isinstance, call:logger.warning, call:type, call:payload.get, call:int, call:pagination.get, call:logger.info, call:len | dep: logging, typing, requests, media_library_viewer_api.clients.http_timeout
@@ -12,10 +12,10 @@ Provides external service integration clients (API wrappers and command executor
 - jellyfin.py | Wraps the Jellyfin/Emby HTTP API to provide methods for fetching users, libraries, media items, playback sessions, and image URLs as plain Python dictionaries. | exp: class:JellyfinClient, method:__init__(self, base_url: str, api_key: str, timeout), call:base_url.rstrip, call:self.base_url.endswith, call:http_timeout, call:requests.Session, call:self.session.headers.update, raise:ValueError, method:get(self, path: str, **params: Any) → Any, call:params.items, call:logger.debug, call:sorted, call:clean_params.keys, call:self.session.get, call:response.raise_for_status, call:logger.warning, call:response.json, raise:requests.HTTPError, method:users(self) → list[dict[str, Any]], call:self.get, call:logger.info, call:len, method:resolve_user_id(self, identifier: str | None) → str, call:self.users, call:any, call:str, call:u.get, call:next, call:logger.info, call:logger.warning, raise:RuntimeError, method:libraries(self, user_id: str) → list[dict[str, Any]], call:self.get(f"/Users/{user_id}/Views").get, call:logger.info, call:len, method:items(self, user_id: str, parent_id, start_index, limit, search, include_item_types, recursive, sort_by, sort_order) → dict[str, Any], call:logger.debug, call:self.get, call:str(recursive).lower, method:item_count(self, user_id: str, include_item_types: str, parent_id) → int, call:self.get, call:int, call:response.get, call:logger.debug, method:media_counts(self, user_id: str) → dict[str, int], call:self.item_count, method:library_item_counts(self, user_id: str, libraries: list[dict[str, Any]]) → list[dict[str, Any]], call:lib.get, call:self.item_count, call:results.append, method:sessions(self, active_within_seconds) → list[dict[str, Any]], call:self.get, call:cast, call:isinstance, method:active_sessions(self, active_within_seconds) → list[dict[str, Any]], call:self.sessions, call:session.get, call:logger.info, call:len, method:image_url(self, item_id: str, image_type) → str | dep: logging, typing, requests, media_library_viewer_api.clients.http_timeout
 - jellyseerr.py | HTTP API client wrapper for Jellyseerr to fetch user data and enrich Jellyfin user lists. | exp: class:JellyseerrClient, method:__init__(self, base_url: str, api_key: str, timeout), call:base_url.rstrip, call:self.base_url.endswith, call:http_timeout, call:requests.Session, call:self.session.headers.update, raise:ValueError, method:get(self, path: str, **params: Any) → Any, call:params.items, call:logger.debug, call:sorted, call:clean_params.keys, call:self.session.get, call:response.raise_for_status, call:logger.warning, call:response.json, raise:requests.HTTPError, method:absolute_url(self, path: str | None) → str, call:path.startswith, method:jellyfin_users(self) → list[dict[str, Any]], call:self.get, call:isinstance, call:logger.info, call:len, call:payload.get, method:users(self, page_size) → list[dict[str, Any]], call:max, call:int, call:self.get, call:isinstance, call:payload.get, call:results.extend, call:page_info.get, call:logger.debug, call:len, call:logger.info | dep: logging, typing, requests, media_library_viewer_api.clients.http_timeout
 - local.py | Provides a local command execution client that mirrors remote SSH helpers to run POSIX shell commands, list directories, stat paths, and run ffprobe on the API host for built-in local monitoring. | exp: class:CommandResult, class:LocalCommandClient, method:__init__(self, timeout), method:run(self, command: str, timeout) → CommandResult, call:logger.debug, call:subprocess.run, call:CommandResult, call:logger.warning, call:result.stderr.strip, call:result.stdout.strip, method:list_dir(self, path: str) → CommandResult, call:shlex.quote, call:self.run, method:stat_path(self, path: str) → CommandResult, call:shlex.quote, call:self.run, method:ffprobe_json(self, path: str) → dict[str, object], call:shlex.quote, call:self.run, call:json.loads, raise:RuntimeError | dep: json, logging, posixpath, shlex, subprocess, dataclasses
-- qbittorrent.py | Minimal read-only API client for qBittorrent that handles authenticated session management to fetch sync data. | exp: class:QbittorrentClient, method:__init__(self, base_url: str, username: str, password: str, timeout) → None, call:base_url.rstrip, call:self.base_url.endswith, call:http_timeout, call:requests.Session, raise:ValueError, method:_login(self) → None, call:self._session.post, call:resp.raise_for_status, call:resp.text.strip, call:bool, call:resp.cookies.get, call:logger.info, raise:RuntimeError, method:_get(self, path: str, **params: Any) → dict[str, Any], call:self._login, call:self._session.get, call:logger.debug, call:resp.raise_for_status, call:resp.json, method:maindata(self) → dict[str, Any], call:self._get | dep: logging, typing, requests, media_library_viewer_api.clients.http_timeout
+- qbittorrent.py | Minimal read-only qBittorrent Web API client that manages authenticated session cookies to fetch torrent data. | exp: class:QbittorrentClient, method:__init__(self, base_url: str, username: str, password: str, timeout) → None, call:base_url.rstrip, call:self.base_url.endswith, call:http_timeout, call:requests.Session, raise:ValueError, method:_login(self) → None, call:self._session.post, call:resp.raise_for_status, call:resp.text.strip, call:bool, call:resp.cookies.get, call:logger.info, raise:RuntimeError, method:_get(self, path: str, **params: Any) → dict[str, Any], call:self._login, call:self._session.get, call:logger.debug, call:resp.raise_for_status, call:resp.json, method:maindata(self) → dict[str, Any], call:self._get | dep: logging, typing, requests, media_library_viewer_api.clients.http_timeout
 - ssh.py | Provides an SSH client wrapper for remote filesystem inspection and media analysis using paramiko, with POSIX shell command execution and host key management. | exp: class:CommandResult, class:RemoteSSHClient, method:__init__(self, host: str, username: str, port, key_filename, private_key, private_key_passphrase, password, known_hosts_path, timeout), raise:ValueError, method:connect(self) → paramiko.SSHClient, call:paramiko.SSHClient, call:client.load_system_host_keys, call:Path, call:bool, call:has_known_host, call:known_hosts_file.is_file, call:client.load_host_keys, call:client.set_missing_host_key_policy, call:paramiko.RejectPolicy, call:paramiko.AutoAddPolicy, call:self._load_private_key, call:client.connect, call:str(exc).lower, call:known_hosts_file.parent.mkdir, call:client.save_host_keys, raise:RuntimeError, method:close(self) → None, call:self._client.close, method:run(self, command: str, timeout) → CommandResult, call:self.connect, call:shlex.quote, call:logger.debug, call:client.exec_command, call:stdout.channel.recv_exit_status, call:CommandResult, call:stdout.read().decode, call:stderr.read().decode, call:logger.warning, call:result.stderr.strip, call:result.stdout.strip, method:list_dir(self, path: str) → CommandResult, call:shlex.quote, call:self.run, call:logger.info, method:stat_path(self, path: str) → CommandResult, call:shlex.quote, call:self.run, call:logger.info, method:ffprobe_json(self, path: str) → dict[str, Any], call:shlex.quote, call:self.run, call:logger.info, call:json.loads, raise:RuntimeError | dep: json, logging, posixpath, shlex, dataclasses, io, pathlib, typing, paramiko, media_library_viewer_api.services.known_hosts
 ## arch
-Adapter/wrapper pattern with each client encapsulating service-specific communication (HTTP REST, SSH, local shell) behind a uniform interface returning plain Python data structures.
+Client-wrapper pattern with per-service classes encapsulating authentication, pagination, and response normalization; consistent dictionary-based data contracts across clients.
 ## tags
 call:logger.info, error, call:logger.debug, call:self.get, client, init, timeout, call:logger.warning
 ## symbols