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/handlers/koreader.go

@@ -264,8 +264,8 @@ func (h *KOReaderHandler) resolveBookToMediaItem(c echo.Context, deviceID pgtype
 			return alias.MediaItemID, alias.ConfidenceScore.Float64
 		}
 
-		// Try to find by file path
-		mediaItem, err := h.db.GetMediaItemByFilePath(ctx, book.FilePath)
+		// Try to find by file path (search any library)
+		mediaItem, err := h.db.GetMediaItemByFilePathAnyLibrary(ctx, book.FilePath)
 		if err == nil {
 			// Create new alias
 			confidence := 0.7

internal/handlers/scanner.go

@@ -266,6 +266,7 @@ func (h *Handler) StartWatchModeForLibrary(ctx context.Context, libraryID pgtype
 	}
 
 	scanner.SetAdminID(adminID)
+	scanner.SetLibraryID(libraryID)
 	scanner.WatchChanges(h.watchModeCtx)
 
 	h.watchingLibraries[libraryIDStr] = true
@@ -382,7 +383,7 @@ func (h *Handler) StartWatchModeForAllLibraries(ctx context.Context) error {
 
 	for _, library := range libraries {
 		libraryIDStr := fmt.Sprintf("%x", library.ID.Bytes)
-		if err := h.StartWatchModeForLibrary(ctx, library.ID, library.ID); err != nil {
+		if err := h.StartWatchModeForLibrary(ctx, library.ID, library.CreatedByAdminID); err != nil {
 			fmt.Printf("Warning: failed to start watch mode for library %s: %v\n", libraryIDStr, err)
 			continue
 		}