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/lastfm.py

@@ -1,28 +0,0 @@
-from dataclasses import dataclass
-from typing import Any
-
-
-@dataclass
-class SimilarArtistEntry:
-    artisthash: str
-    name: str
-    weight: float
-    scrobbles: int
-    listeners: int
-
-
-@dataclass
-class SimilarArtist:
-    artisthash: str
-    similar_artists: list[SimilarArtistEntry]
-
-
-    def get_artist_hash_set(self) -> set[str]:
-        """
-        Returns a set of similar artists.
-        """
-        if not self.similar_artists:
-            return set()
-
-        # INFO: 
-        return set(a['artisthash'] for a in self.similar_artists)