feat: implement multiple folder ebook scanner and API handlers

- Create EbookScanner service with multiple folder support
- Update scanner to handle array of folder paths instead of single path
- Add EPUB metadata extraction for rich ebook information
- Implement folder monitoring with fsnotify for real-time updates
- Add API endpoints for folder management:
  - POST /api/auth/ebook-folders (add folder)
  - GET /api/auth/ebook-folders (list folders)
  - DELETE /api/auth/ebook-folders/:folderPath (remove folder)
- Update scanner endpoints to accept folder_paths array
- Add go-epub and fsnotify dependencies for metadata extraction and file watching

backend/go.mod

@@ -3,9 +3,10 @@ module bookmann
 go 1.25
 
 require (
+	github.com/ArcadiaLin/go-epub v0.1.1
+	github.com/fsnotify/fsnotify v1.9.0
 	github.com/go-playground/validator/v10 v10.30.1
-
-
+	github.com/golang-jwt/jwt v3.2.2+incompatible
 	github.com/google/uuid v1.4.0
 	github.com/jackc/pgx/v5 v5.4.3
 	github.com/labstack/echo/v4 v4.11.3
@@ -16,7 +17,6 @@ require (
 	github.com/gabriel-vasile/mimetype v1.4.12 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
-	github.com/golang-jwt/jwt v3.2.2+incompatible // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a // indirect
 	github.com/jackc/puddle/v2 v2.2.1 // indirect