feat(nfo): add minimal NFO fallback when TMDB fails

- Add create_minimal_nfo() method to NFOService for fallback when TMDB lookup fails
- Update API endpoints (single and batch) to use minimal NFO fallback on TMDBAPIError
- Document fallback behavior in NFO_GUIDE.md section 3.6
- Add unit tests for minimal NFO creation (11 tests passing)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/core/services/nfo_service.py

@@ -20,6 +20,7 @@ from src.core.services.tmdb_client import TMDBAPIError, TMDBClient
 from src.core.utils.image_downloader import ImageDownloader
 from src.core.utils.nfo_generator import generate_tvshow_nfo
 from src.core.utils.nfo_mapper import tmdb_to_nfo_model
+from src.core.entities.nfo_models import TVShowNFO
 
 logger = logging.getLogger(__name__)
 
@@ -423,6 +424,62 @@ class NFOService:
             logger.error("Error parsing NFO file %s: %s", nfo_path, e)
         
         return result
+
+    def parse_nfo_year(self, nfo_path: Path) -> Optional[int]:
+        """Parse year from an existing NFO file.
+        
+        Extracts year from <year> or <premiered> elements.
+        
+        Args:
+            nfo_path: Path to tvshow.nfo file
+            
+        Returns:
+            Year as integer if found, None otherwise.
+            
+        Example:
+            >>> year = nfo_service.parse_nfo_year(Path("/anime/series/tvshow.nfo"))
+            >>> print(year)
+            2013
+        """
+        if not nfo_path.exists():
+            logger.debug("NFO file not found: %s", nfo_path)
+            return None
+        
+        try:
+            tree = etree.parse(str(nfo_path))
+            root = tree.getroot()
+            
+            # Try <year> element first
+            year_elem = root.find(".//year")
+            if year_elem is not None and year_elem.text:
+                try:
+                    year = int(year_elem.text)
+                    if 1900 <= year <= 2100:
+                        logger.debug("Found year in NFO: %d", year)
+                        return year
+                except ValueError:
+                    pass
+            
+            # Fallback: try <premiered> element (format: YYYY-MM-DD)
+            premiered_elem = root.find(".//premiered")
+            if premiered_elem is not None and premiered_elem.text:
+                if premiered_elem.text and len(premiered_elem.text) >= 4:
+                    try:
+                        year = int(premiered_elem.text[:4])
+                        if 1900 <= year <= 2100:
+                            logger.debug("Found year from premiered in NFO: %d", year)
+                            return year
+                    except ValueError:
+                        pass
+            
+            logger.debug("No year found in NFO: %s", nfo_path)
+            
+        except etree.XMLSyntaxError as e:
+            logger.error("Invalid XML in NFO file %s: %s", nfo_path, e)
+        except Exception as e:  # pylint: disable=broad-except
+            logger.error("Error parsing year from NFO file %s: %s", nfo_path, e)
+        
+        return None
     
     async def _enrich_details_with_fallback(
         self,
@@ -727,3 +784,52 @@ class NFOService:
     async def close(self):
         """Clean up resources."""
         await self.tmdb_client.close()
+    
+    async def create_minimal_nfo(
+        self,
+        serie_name: str,
+        serie_folder: str,
+        year: Optional[int] = None
+    ) -> Path:
+        """Create minimal tvshow.nfo when TMDB lookup fails.
+        
+        Creates a basic NFO with just the title (and year if available)
+        so the series is tracked even without TMDB metadata.
+        
+        Args:
+            serie_name: Name of the series (may include year in parentheses)
+            serie_folder: Series folder name
+            year: Optional release year
+            
+        Returns:
+            Path to created NFO file
+            
+        Raises:
+            FileNotFoundError: If series folder doesn't exist
+        """
+        # Extract year from name if not provided
+        clean_name, extracted_year = self._extract_year_from_name(serie_name)
+        if year is None and extracted_year is not None:
+            year = extracted_year
+        
+        folder_path = self.anime_directory / serie_folder
+        if not folder_path.exists():
+            logger.info("Creating series folder: %s", folder_path)
+            folder_path.mkdir(parents=True, exist_ok=True)
+        
+        # Create minimal NFO model with just title and year
+        nfo_model = TVShowNFO(
+            title=clean_name,
+            year=year,
+            plot=f"No metadata available for {clean_name}. TMDB lookup failed."
+        )
+        
+        # Generate XML
+        nfo_xml = generate_tvshow_nfo(nfo_model)
+        
+        # Save NFO file
+        nfo_path = folder_path / "tvshow.nfo"
+        nfo_path.write_text(nfo_xml, encoding="utf-8")
+        logger.info("Created minimal NFO (no TMDB): %s", nfo_path)
+        
+        return nfo_path