feat: Add NFO metadata infrastructure (Task 3 - partial)

- Created TMDB API client with async requests, caching, and retry logic
- Implemented NFO XML generator for Kodi/XBMC format
- Created image downloader for poster/logo/fanart with validation
- Added NFO service to orchestrate metadata creation
- Added NFO-related configuration settings
- Updated requirements.txt with aiohttp, lxml, pillow
- Created unit tests (need refinement due to implementation mismatch)

Components created:
- src/core/services/tmdb_client.py (270 lines)
- src/core/services/nfo_service.py (390 lines)
- src/core/utils/nfo_generator.py (180 lines)
- src/core/utils/image_downloader.py (296 lines)
- tests/unit/test_tmdb_client.py
- tests/unit/test_nfo_generator.py
- tests/unit/test_image_downloader.py

Note: Tests need to be updated to match actual implementation APIs.
Dependencies installed: aiohttp, lxml, pillow

src/config/settings.py

@@ -72,6 +72,43 @@ class Settings(BaseSettings):
         default=3,
         validation_alias="RETRY_ATTEMPTS"
     )
+    
+    # NFO / TMDB Settings
+    tmdb_api_key: Optional[str] = Field(
+        default=None,
+        validation_alias="TMDB_API_KEY",
+        description="TMDB API key for scraping TV show metadata"
+    )
+    nfo_auto_create: bool = Field(
+        default=False,
+        validation_alias="NFO_AUTO_CREATE",
+        description="Automatically create NFO files when scanning series"
+    )
+    nfo_update_on_scan: bool = Field(
+        default=False,
+        validation_alias="NFO_UPDATE_ON_SCAN",
+        description="Update existing NFO files when scanning series"
+    )
+    nfo_download_poster: bool = Field(
+        default=True,
+        validation_alias="NFO_DOWNLOAD_POSTER",
+        description="Download poster.jpg when creating NFO"
+    )
+    nfo_download_logo: bool = Field(
+        default=True,
+        validation_alias="NFO_DOWNLOAD_LOGO",
+        description="Download logo.png when creating NFO"
+    )
+    nfo_download_fanart: bool = Field(
+        default=True,
+        validation_alias="NFO_DOWNLOAD_FANART",
+        description="Download fanart.jpg when creating NFO"
+    )
+    nfo_image_size: str = Field(
+        default="original",
+        validation_alias="NFO_IMAGE_SIZE",
+        description="Image size to download (original, w500, etc.)"
+    )
 
     @property
     def allowed_origins(self) -> list[str]: