scanner: fix library isolation, file mtime, force rescan, and deletion handling

Fix 1 - File modification time for created_at:
- Get file.ModTime() in processMediaFile and pass to CreateMediaItem
- Modified SQL INSERT to include created_at column

Fix 2 - Force rescan UPDATE instead of DELETE+INSERT:
- Changed force rescan logic to call updateMediaItem instead of delete + create
- Preserves created_at timestamp on force rescan

Fix 3 - GetMediaItemByFilePath filters by library_id:
- Added library_id to WHERE clause in SQL query
- Created GetMediaItemByFilePathAnyLibrary for cross-library lookups (KOReader)
- Added SetLibraryID method to MediaScanner
- Updated handler to call SetLibraryID for watch mode

Fix 4 - File deletion handling with persistent logging:
- Added fsnotify.Remove handler in WatchChanges
- Added orphan cleanup in ScanFolders after scan completes
- Created scanner_logger.go with daily log rotation (7 days)
- Logs to /app/logs/scanner-deletes-YYYY-MM-DD.log and scanner-errors-YYYY-MM-DD.log
- Individual deletes with enhanced safety logging

Note: Integration tests can now safely scan /app/uploads because
GetMediaItemByFilePath now filters by library_id, preventing
cross-library interference.

internal/database/querier.go

@@ -175,7 +175,8 @@ type Querier interface {
 	GetMediaHighlight(ctx context.Context, id pgtype.UUID) (MediaHighlights, error)
 	GetMediaHighlights(ctx context.Context, arg GetMediaHighlightsParams) ([]MediaHighlights, error)
 	GetMediaItem(ctx context.Context, id pgtype.UUID) (MediaItems, error)
-	GetMediaItemByFilePath(ctx context.Context, filePath string) (MediaItems, error)
+	GetMediaItemByFilePath(ctx context.Context, arg GetMediaItemByFilePathParams) (MediaItems, error)
+	GetMediaItemByFilePathAnyLibrary(ctx context.Context, filePath string) (MediaItems, error)
 	// ============================================
 	// KOREADER SYNC PROTOCOL
 	// ============================================