chore: remove dead machine-level Jellyfin/Jellyseerr fields

Follow-up #1 to the service-registry change. Jellyfin/Jellyseerr now resolve
from the service registry, so the machine-level app fields are dead config.

- dependencies.py: drop dead _jellyseerr_client_for; simplify _resolve_machine
  to SSH-only.
- settings_store.py + routers/settings.py: remove jellyfin_*/jellyseerr_* from
  machine default config, get_machine_config, normalization, row mappers, and
  MachineInput.
- frontend types + Settings.tsx: drop the fields and the Jellyfin/Jellyseerr
  form sections + service options.
- Update frontend test fixtures.

Existing DB rows may still carry these keys in config_json; they are inert and
drop on the next machine save. Verification: backend ruff clean, pytest 222;
frontend lint 0 errors, build success, 70 tests.

backend/src/media_library_viewer_api/services/settings_store.py

@@ -44,11 +44,6 @@ def _default_local_machine() -> dict[str, Any]:
         "password": "",
         "media_root": settings.media_root,
         "path_prefix": settings.path_prefix,
-        "jellyfin_url": "",
-        "jellyfin_user_id": "",
-        "jellyfin_api_key": "",
-        "jellyseerr_url": "",
-        "jellyseerr_api_key": "",
         "node_exporter_enabled": False,
         "node_exporter_port": 9100,
         "node_exporter_scrape_host": "",
@@ -306,11 +301,6 @@ class SettingsStore:
             "password_set": bool(data.get("password")),
             "media_root": data.get("media_root", ""),
             "path_prefix": data.get("path_prefix", ""),
-            "jellyfin_url": data.get("jellyfin_url", ""),
-            "jellyfin_user_id": data.get("jellyfin_user_id", ""),
-            "jellyfin_api_key_set": bool(data.get("jellyfin_api_key")),
-            "jellyseerr_url": data.get("jellyseerr_url", ""),
-            "jellyseerr_api_key_set": bool(data.get("jellyseerr_api_key")),
             "node_exporter_enabled": bool(data.get("node_exporter_enabled", False)),
             "node_exporter_port": int(data.get("node_exporter_port", 9100) or 9100),
             "node_exporter_scrape_host": data.get("node_exporter_scrape_host", ""),
@@ -360,17 +350,6 @@ class SettingsStore:
         password = str(password or "")
         media_root = _current_str("media_root")
         path_prefix = _current_str("path_prefix")
-        jellyfin_url = _current_str("jellyfin_url")
-        jellyfin_user_id = _current_str("jellyfin_user_id")
-        jellyfin_api_key = payload.get("jellyfin_api_key")
-        if jellyfin_api_key in (None, ""):
-            jellyfin_api_key = (current or {}).get("jellyfin_api_key", "")
-        jellyfin_api_key = str(jellyfin_api_key or "")
-        jellyseerr_url = _current_str("jellyseerr_url")
-        jellyseerr_api_key = payload.get("jellyseerr_api_key")
-        if jellyseerr_api_key in (None, ""):
-            jellyseerr_api_key = (current or {}).get("jellyseerr_api_key", "")
-        jellyseerr_api_key = str(jellyseerr_api_key or "")
         node_exporter_enabled = bool(
             payload.get("node_exporter_enabled")
             if payload.get("node_exporter_enabled") is not None
@@ -402,11 +381,6 @@ class SettingsStore:
             "password": password,
             "media_root": media_root,
             "path_prefix": path_prefix,
-            "jellyfin_url": jellyfin_url,
-            "jellyfin_user_id": jellyfin_user_id,
-            "jellyfin_api_key": jellyfin_api_key,
-            "jellyseerr_url": jellyseerr_url,
-            "jellyseerr_api_key": jellyseerr_api_key,
             "node_exporter_enabled": node_exporter_enabled,
             "node_exporter_port": node_exporter_port,
             "node_exporter_scrape_host": node_exporter_scrape_host,
@@ -430,11 +404,6 @@ class SettingsStore:
             "password": "",
             "media_root": machine["media_root"],
             "path_prefix": machine["path_prefix"],
-            "jellyfin_url": machine["jellyfin_url"],
-            "jellyfin_user_id": machine["jellyfin_user_id"],
-            "jellyfin_api_key": machine["jellyfin_api_key"],
-            "jellyseerr_url": machine["jellyseerr_url"],
-            "jellyseerr_api_key": machine["jellyseerr_api_key"],
             "node_exporter_enabled": machine["node_exporter_enabled"],
             "node_exporter_port": machine["node_exporter_port"],
             "node_exporter_scrape_host": machine["node_exporter_scrape_host"],
@@ -520,11 +489,6 @@ class SettingsStore:
             "password": data.get("password", ""),
             "media_root": data.get("media_root", ""),
             "path_prefix": data.get("path_prefix", ""),
-            "jellyfin_url": data.get("jellyfin_url", ""),
-            "jellyfin_user_id": data.get("jellyfin_user_id", ""),
-            "jellyfin_api_key": data.get("jellyfin_api_key", ""),
-            "jellyseerr_url": data.get("jellyseerr_url", ""),
-            "jellyseerr_api_key": data.get("jellyseerr_api_key", ""),
             "node_exporter_enabled": bool(data.get("node_exporter_enabled", False)),
             "node_exporter_port": int(data.get("node_exporter_port", 9100) or 9100),
             "node_exporter_scrape_host": data.get("node_exporter_scrape_host", ""),
@@ -564,11 +528,6 @@ class SettingsStore:
             "password": machine["password"],
             "media_root": machine["media_root"],
             "path_prefix": machine["path_prefix"],
-            "jellyfin_url": machine["jellyfin_url"],
-            "jellyfin_user_id": machine["jellyfin_user_id"],
-            "jellyfin_api_key": machine["jellyfin_api_key"],
-            "jellyseerr_url": machine["jellyseerr_url"],
-            "jellyseerr_api_key": machine["jellyseerr_api_key"],
             "node_exporter_enabled": machine["node_exporter_enabled"],
             "node_exporter_port": machine["node_exporter_port"],
             "node_exporter_scrape_host": machine["node_exporter_scrape_host"],