Reorganize repository structure for better organization

- Move backend code to swingmusic/ folder
- Move client applications to root level (swingmusic-android, swingmusic-desktop, swingmusic-webclient)
- Remove intermediate backend/ and clients/ folders
- Update README with new folder structure and setup instructions
- Clean and organized repository layout

src/swingmusic/models/enums.py

@@ -1,6 +0,0 @@
-class FavType:
-    """Favorite types enum"""
-
-    track = "track"
-    album = "album"
-    artist = "artist"