feat: Add NFO configuration settings (Task 7)

- Added NFOConfig model with TMDB API key, auto-create, media downloads, image size settings
- Created NFO settings section in UI with form fields and validation
- Implemented nfo-config.js module for loading, saving, and testing TMDB connection
- Added TMDB API key validation endpoint (POST /api/config/tmdb/validate)
- Integrated NFO config into AppConfig and ConfigUpdate models
- Added 5 unit tests for NFO config model validation
- Added API test for TMDB validation endpoint
- All 16 config model tests passing, all 10 config API tests passing
- Documented in docs/task7_status.md (100% complete)

src/server/models/config.py

@@ -54,6 +54,43 @@ class LoggingConfig(BaseModel):
         return lvl
 
 
+class NFOConfig(BaseModel):
+    """NFO metadata configuration."""
+
+    tmdb_api_key: Optional[str] = Field(
+        default=None, description="TMDB API key for metadata scraping"
+    )
+    auto_create: bool = Field(
+        default=False, description="Auto-create NFO files for new series"
+    )
+    update_on_scan: bool = Field(
+        default=False, description="Update existing NFO files on rescan"
+    )
+    download_poster: bool = Field(
+        default=True, description="Download poster.jpg"
+    )
+    download_logo: bool = Field(
+        default=True, description="Download logo.png"
+    )
+    download_fanart: bool = Field(
+        default=True, description="Download fanart.jpg"
+    )
+    image_size: str = Field(
+        default="original", description="Image size (original or w500)"
+    )
+
+    @field_validator("image_size")
+    @classmethod
+    def validate_image_size(cls, v: str) -> str:
+        allowed = {"original", "w500"}
+        size = (v or "").lower()
+        if size not in allowed:
+            raise ValueError(
+                f"invalid image size: {v}. Must be 'original' or 'w500'"
+            )
+        return size
+
+
 class ValidationResult(BaseModel):
     """Result of a configuration validation attempt."""
 
@@ -77,6 +114,7 @@ class AppConfig(BaseModel):
     )
     logging: LoggingConfig = Field(default_factory=LoggingConfig)
     backup: BackupConfig = Field(default_factory=BackupConfig)
+    nfo: NFOConfig = Field(default_factory=NFOConfig)
     other: Dict[str, object] = Field(
         default_factory=dict, description="Arbitrary other settings"
     )
@@ -114,6 +152,7 @@ class ConfigUpdate(BaseModel):
     scheduler: Optional[SchedulerConfig] = None
     logging: Optional[LoggingConfig] = None
     backup: Optional[BackupConfig] = None
+    nfo: Optional[NFOConfig] = None
     other: Optional[Dict[str, object]] = None
 
     def apply_to(self, current: AppConfig) -> AppConfig:
@@ -128,6 +167,8 @@ class ConfigUpdate(BaseModel):
             data["logging"] = self.logging.model_dump()
         if self.backup is not None:
             data["backup"] = self.backup.model_dump()
+        if self.nfo is not None:
+            data["nfo"] = self.nfo.model_dump()
         if self.other is not None:
             merged = dict(current.other or {})
             merged.update(self.other)