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/server/api/nfo.py

@@ -144,6 +144,27 @@ async def batch_create_nfo(
                     nfo_path=str(nfo_path)
                 )
                 
+            except TMDBAPIError as e:
+                logger.warning("TMDB API error for %s, creating minimal fallback: %s", serie_id, e)
+                # TMDB failed, create minimal NFO
+                try:
+                    serie_folder = serie.ensure_folder_with_year()
+                except Exception:
+                    serie_folder = serie_folder
+                
+                serie_name = serie.name or serie_folder
+                nfo_path = await nfo_service.create_minimal_nfo(
+                    serie_name=serie_name,
+                    serie_folder=serie_folder
+                )
+                
+                return NFOBatchResult(
+                    serie_id=serie_id,
+                    serie_folder=serie_folder,
+                    success=True,
+                    message="Created minimal NFO (TMDB lookup failed)",
+                    nfo_path=str(nfo_path)
+                )
             except Exception as e:
                 logger.error(
                     f"Error creating NFO for {serie_id}: {e}",
@@ -429,11 +450,42 @@ async def create_nfo(
     except HTTPException:
         raise
     except TMDBAPIError as e:
-        logger.warning("TMDB API error creating NFO for %s: %s", serie_id, e)
-        raise HTTPException(
-            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
-            detail=f"TMDB API error: {str(e)}"
-        ) from e
+        logger.warning("TMDB API error for %s, creating minimal fallback: %s", serie_id, e)
+        # TMDB failed, create minimal NFO with just folder name
+        try:
+            serie_folder = serie.ensure_folder_with_year()
+        except Exception:
+            serie_folder = serie_folder
+        
+        folder_path = Path(settings.anime_directory) / serie_folder
+        serie_name_fallback = request.serie_name or serie.name or serie_folder
+        
+        nfo_path = await nfo_service.create_minimal_nfo(
+            serie_name=serie_name_fallback,
+            serie_folder=serie_folder,
+            year=year
+        )
+        
+        # Check media files (will likely be empty)
+        media_status = check_media_files(folder_path)
+        file_paths = get_media_file_paths(folder_path)
+        
+        media_files = MediaFilesStatus(
+            has_poster=media_status.get("poster", False),
+            has_logo=media_status.get("logo", False),
+            has_fanart=media_status.get("fanart", False),
+            poster_path=str(file_paths["poster"]) if file_paths.get("poster") else None,
+            logo_path=str(file_paths["logo"]) if file_paths.get("logo") else None,
+            fanart_path=str(file_paths["fanart"]) if file_paths.get("fanart") else None
+        )
+        
+        return NFOCreateResponse(
+            serie_id=serie_id,
+            serie_folder=serie_folder,
+            nfo_path=str(nfo_path),
+            media_files=media_files,
+            message="Created minimal NFO (TMDB lookup failed)"
+        )
     except Exception as e:
         logger.error(
             f"Error creating NFO for {serie_id}: {e}",