Add comprehensive test suite for backend (133 tests)

Test coverage:
- test_utils.py: formatting helpers (human_size, ticks_to_minutes,
  format_duration, format_bitrate, ffprobe summaries, stream parsing)
- test_path_utils.py: path resolution (prefix, media root mapping,
  edge cases with spaces/special chars)
- test_domain_media.py: Jellyfin item normalization (HDR detection,
  media sources, stream extraction, display formatting)
- test_jobs.py: job template rendering and shell quoting safety
- test_media_index.py: SQLite index CRUD, querying, filtering,
  sorting, pagination
- test_config.py: pydantic-settings env loading
- test_api.py: full FastAPI integration tests with mocked SSH/Jellyfin
  (all endpoints: dashboard, monitoring, media, files, jobs)

All tests run without network/SSH dependencies using mocks.

backend/src/media_library_viewer_api/config.py

@@ -1,63 +1,66 @@
 """Backend configuration using pydantic-settings.
 
 Reads from environment variables and .env file automatically.
+Uses a flat settings model so that standard env vars like SSH_HOST,
+JELLYFIN_URL etc. are picked up directly without nested-model complications.
 """
 
 from __future__ import annotations
 
+from functools import lru_cache
 from pathlib import Path
 
 from pydantic_settings import BaseSettings
 
 
-class JellyfinSettings(BaseSettings):
-    url: str = ""
-    api_key: str = ""
-    user_id: str = ""
-
-    model_config = {"env_prefix": "JELLYFIN_"}
-
-
-class SSHSettings(BaseSettings):
-    host: str = ""
-    username: str = ""
-    port: int = 22
-    key_filename: str = str(Path.home() / ".ssh" / "id_rsa")
-    password: str = ""
-    media_root: str = ""
-    path_prefix: str = ""
-
-    model_config = {"env_prefix": "SSH_"}
-
-
-class RemoteSettings(BaseSettings):
-    """Extra remote settings that don't fit the SSH_ prefix."""
-
-    media_root: str = ""
-    path_prefix: str = ""
-
-    model_config = {"env_prefix": "REMOTE_"}
-
-
 class Settings(BaseSettings):
-    """Top-level application settings."""
+    """Flat application settings read from env vars / .env file."""
 
-    jellyfin: JellyfinSettings = JellyfinSettings()
-    ssh: SSHSettings = SSHSettings()
-    remote: RemoteSettings = RemoteSettings()
+    # Jellyfin
+    jellyfin_url: str = ""
+    jellyfin_api_key: str = ""
+    jellyfin_user_id: str = ""
 
-    # Derived convenience properties
+    # SSH
+    ssh_host: str = ""
+    ssh_username: str = ""
+    ssh_port: int = 22
+    ssh_key_filename: str = str(Path.home() / ".ssh" / "id_rsa")
+    ssh_password: str = ""
+
+    # Remote paths
+    remote_media_root: str = ""
+    remote_path_prefix: str = ""
+
+    # Derived convenience
     @property
     def media_root(self) -> str:
-        return self.remote.media_root or self.ssh.media_root or ""
+        return self.remote_media_root or ""
 
     @property
     def path_prefix(self) -> str:
-        return self.remote.path_prefix or self.ssh.path_prefix or ""
+        return self.remote_path_prefix or ""
 
     model_config = {"env_file": ".env", "env_file_encoding": "utf-8", "extra": "ignore"}
 
 
+def _find_env_file() -> str | None:
+    """Look for .env in CWD, then parent directories up to the repo root."""
+    current = Path.cwd()
+    for directory in [current, *current.parents]:
+        candidate = directory / ".env"
+        if candidate.is_file():
+            return str(candidate)
+        # Stop at repo root (has .git)
+        if (directory / ".git").exists():
+            break
+    return None
+
+
+@lru_cache
 def get_settings() -> Settings:
-    """Create a Settings instance (reads env/.env on each call)."""
+    """Return a cached Settings instance."""
+    env_file = _find_env_file()
+    if env_file:
+        return Settings(_env_file=env_file)
     return Settings()