feat(setup): track unresolved folders for manual key resolution

When SetupService cannot auto-resolve a provider key for an anime folder,
the folder is now tracked in the new 'unresolved_folders' table instead of
being silently skipped. Users can then resolve these via the new API:

- GET /api/setup/unresolved - list unresolved folders with search suggestions
- POST /api/setup/unresolved/{folder}/resolve - provide key to resolve folder

The SetupService.run() now:
- Tracks unresolved folders instead of skipping them
- Re-creates AnimeSeries for previously unresolved folders that are now resolved
- Includes unresolved count in logs

New files:
- src/server/api/setup_endpoints.py - API endpoints for unresolved management
- tests/unit/test_unresolved_folder_service.py - service and model tests

Modified:
- src/server/database/models.py - add UnresolvedFolder model
- src/server/database/service.py - add UnresolvedFolderService
- src/server/services/setup_service.py - track unresolved folders
- src/server/fastapi_app.py - include setup router

src/server/database/service.py

@@ -34,6 +34,7 @@ from src.server.database.models import (
     AnimeSeries,
     DownloadQueueItem,
     Episode,
+    UnresolvedFolder,
     UserSession,
 )
 
@@ -1364,3 +1365,176 @@ class UserSessionService:
         
         return new_session
 
+
+# ============================================================================
+# Unresolved Folder Service
+# ============================================================================
+
+
+class UnresolvedFolderService:
+    """Service for tracking and resolving folders that couldn't be auto-resolved.
+    
+    During initial setup, some folders may not resolve to a provider key
+    (no search match or multiple ambiguous matches). These are tracked as
+    UnresolvedFolder records and can later be resolved by the user providing
+    the correct provider key.
+    """
+    
+    @staticmethod
+    async def create(
+        db: AsyncSession,
+        folder_name: str,
+        title: str,
+        year: int | None = None,
+        search_attempts: int = 1,
+        last_search_result: str | None = None,
+    ) -> UnresolvedFolder:
+        """Create a new unresolved folder tracking record.
+        
+        Args:
+            db: Database session
+            folder_name: Original filesystem folder name
+            title: Extracted title from folder name
+            year: Extracted release year (optional)
+            search_attempts: Number of search attempts made (default: 1)
+            last_search_result: JSON string of search results for UI (optional)
+        
+        Returns:
+            Created UnresolvedFolder instance
+        """
+        folder = UnresolvedFolder(
+            folder_name=folder_name,
+            title=title,
+            year=year,
+            search_attempts=search_attempts,
+            last_search_result=last_search_result,
+        )
+        db.add(folder)
+        await db.flush()
+        await db.refresh(folder)
+        logger.info(
+            "Created unresolved folder tracking: %s (title=%s, year=%s)",
+            folder_name, title, year
+        )
+        return folder
+    
+    @staticmethod
+    async def get_by_folder_name(
+        db: AsyncSession,
+        folder_name: str,
+    ) -> Optional[UnresolvedFolder]:
+        """Get unresolved folder by folder name.
+        
+        Args:
+            db: Database session
+            folder_name: Filesystem folder name to look up
+        
+        Returns:
+            UnresolvedFolder instance or None if not found
+        """
+        result = await db.execute(
+            select(UnresolvedFolder).where(
+                UnresolvedFolder.folder_name == folder_name
+            )
+        )
+        return result.scalar_one_or_none()
+    
+    @staticmethod
+    async def get_all_unresolved(
+        db: AsyncSession,
+    ) -> list[UnresolvedFolder]:
+        """Get all unresolved folders that haven't been resolved yet.
+        
+        Args:
+            db: Database session
+        
+        Returns:
+            List of unresolved UnresolvedFolder instances
+        """
+        result = await db.execute(
+            select(UnresolvedFolder)
+            .where(UnresolvedFolder.provider_key.is_(None))
+            .order_by(UnresolvedFolder.created_at)
+        )
+        return list(result.scalars().all())
+    
+    @staticmethod
+    async def resolve(
+        db: AsyncSession,
+        folder_name: str,
+        provider_key: str,
+    ) -> Optional[UnresolvedFolder]:
+        """Mark an unresolved folder as resolved with the given provider key.
+        
+        Args:
+            db: Database session
+            folder_name: Filesystem folder name to resolve
+            provider_key: Provider key to associate with this folder
+        
+        Returns:
+            Updated UnresolvedFolder instance or None if not found
+        """
+        from datetime import datetime, timezone
+        
+        folder = await UnresolvedFolderService.get_by_folder_name(db, folder_name)
+        if not folder:
+            return None
+        
+        folder.provider_key = provider_key
+        folder.resolved_at = datetime.now(timezone.utc)
+        await db.flush()
+        await db.refresh(folder)
+        logger.info(
+            "Resolved unresolved folder: %s -> key=%s",
+            folder_name, provider_key
+        )
+        return folder
+    
+    @staticmethod
+    async def delete(
+        db: AsyncSession,
+        folder_name: str,
+    ) -> bool:
+        """Delete an unresolved folder record (e.g., after manual add).
+        
+        Args:
+            db: Database session
+            folder_name: Filesystem folder name to delete
+        
+        Returns:
+            True if deleted, False if not found
+        """
+        folder = await UnresolvedFolderService.get_by_folder_name(db, folder_name)
+        if not folder:
+            return False
+        
+        await db.delete(folder)
+        await db.flush()
+        return True
+    
+    @staticmethod
+    async def update_search_result(
+        db: AsyncSession,
+        folder_name: str,
+        search_result: str,
+    ) -> Optional[UnresolvedFolder]:
+        """Update the cached search result for an unresolved folder.
+        
+        Args:
+            db: Database session
+            folder_name: Filesystem folder name to update
+            search_result: JSON string of search results
+        
+        Returns:
+            Updated UnresolvedFolder instance or None if not found
+        """
+        folder = await UnresolvedFolderService.get_by_folder_name(db, folder_name)
+        if not folder:
+            return None
+        
+        folder.search_attempts += 1
+        folder.last_search_result = search_result
+        await db.flush()
+        await db.refresh(folder)
+        return folder
+