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/lib/recipes/because.py

@@ -1,40 +0,0 @@
-from pprint import pprint
-from swingmusic.db.userdata import UserTable
-from swingmusic.lib.recipes import HomepageRoutine
-from swingmusic.lib.recipes.artistmixes import ArtistMixes
-from swingmusic.models.mix import Mix
-from swingmusic.plugins.mixes import MixesPlugin
-from swingmusic.store.homepage import HomepageStore
-
-
-class BecauseYouListened(HomepageRoutine):
-    store_keys = ["because_you_listened_to_artist", "artists_you_might_like"]
-
-    @property
-    def is_valid(self):
-        return MixesPlugin().enabled
-
-    def run(self):
-        users = UserTable.get_all()
-
-        for user in users:
-            entry: dict[str, Mix] = HomepageStore.entries.get(
-                ArtistMixes.store_key
-            ).items.get(user.id)  # type: ignore
-
-            if not entry:
-                continue
-
-            because_you_listened_to_artist, artists_you_might_like = (
-                MixesPlugin().get_because_items(list(entry.values()))
-            )
-
-            if not because_you_listened_to_artist or not artists_you_might_like:
-                continue
-
-            HomepageStore.entries[self.store_keys[0]].items[
-                user.id
-            ] = because_you_listened_to_artist
-            HomepageStore.entries[self.store_keys[1]].items[
-                user.id
-            ] = artists_you_might_like