feat: implement relative path storage and URL resolution for media files

- Add libraryService dependency to CollectionHandler and OPDSHandler for centralized path resolution
- Create internal/utils/mediaurl.go with ResolveMediaURL() function as single source of truth
- Update GetMediaItem and ListMediaItems handlers to return resolved URLs in API responses
- Update collection handlers (GetCollection, TestRules, PreviewCollection) to use resolved cover URLs
- Update progress handler (GetAllProgress) to use resolved cover URLs
- Add library_id to GetCollectionItems SQL query to enable URL resolution
- Refactor media scanner to store relative paths instead of absolute filesystem paths
- Add ResolveMediaPath() to LibraryService for resolving relative paths to absolute paths
- Add ServeFile endpoint at /uploads/library-:id/* for authenticated file serving
- Add MimeTypes map to library_service.go for consistent MIME type handling
- Update DownloadBook handler to use resolved filesystem paths
- Add getRelativePath() helper to MediaScanner for converting absolute to relative paths
- Use strings.EqualFold for case-insensitive path comparisons in zip extraction

This change enables the application to work with relative paths stored in the
database, making it portable across different server environments while
maintaining backward compatibility with existing absolute paths.

internal/handlers/opds.go

@@ -22,16 +22,18 @@ import (
 
 type OPDSHandler struct {
 	db                *database.Queries
+	libraryService    *services.LibraryService
 	conversionService interface {
 		ConvertEPUBToKEPUB(ctx context.Context, mediaItemID pgtype.UUID, epubPath string) (*services.ConvertedKEPUB, error)
 	}
 }
 
-func NewOPDSHandler(db *database.Queries, conversionService interface {
+func NewOPDSHandler(db *database.Queries, libraryService *services.LibraryService, conversionService interface {
 	ConvertEPUBToKEPUB(ctx context.Context, mediaItemID pgtype.UUID, epubPath string) (*services.ConvertedKEPUB, error)
 }) *OPDSHandler {
 	return &OPDSHandler{
 		db:                db,
+		libraryService:    libraryService,
 		conversionService: conversionService,
 	}
 }
@@ -522,13 +524,19 @@ func (h *OPDSHandler) GetCoverImage(c echo.Context) error {
 
 	coverPath := mediaItem.CoverImagePath.String
 
+	// Resolve relative path using library service
+	fullPath, err := h.libraryService.ResolveMediaPath(c.Request().Context(), mediaItem.LibraryID, coverPath)
+	if err != nil {
+		return c.NoContent(http.StatusNoContent)
+	}
+
 	// Check if file exists
-	if _, err := os.Stat(coverPath); os.IsNotExist(err) {
+	if _, err := os.Stat(fullPath); os.IsNotExist(err) {
 		return c.NoContent(http.StatusNoContent)
 	}
 
 	// Open file
-	file, err := os.Open(coverPath)
+	file, err := os.Open(fullPath)
 	if err != nil {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "failed to open cover"})
 	}
@@ -541,7 +549,7 @@ func (h *OPDSHandler) GetCoverImage(c echo.Context) error {
 	}
 
 	// Determine content type
-	ext := strings.ToLower(filepath.Ext(coverPath))
+	ext := strings.ToLower(filepath.Ext(fullPath))
 	contentType := "image/jpeg"
 	if ext == ".png" {
 		contentType = "image/png"