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/crons/__init__.py

@@ -1,31 +0,0 @@
-import time
-import schedule
-
-from swingmusic.crons.mixes import Mixes
-from swingmusic.lib.recipes.recents import RecentlyAdded, RecentlyPlayed
-from swingmusic.lib.recipes.topstreamed import TopArtists
-from swingmusic.utils.threading import background
-
-
-@background
-def start_cron_jobs():
-    """
-    This is the function that triggers the cron jobs.
-    """
-    # NOTE: RecentlyPlayed is not a CRON job, it's triggered here to
-    # populate the values for the very first time.
-    RecentlyPlayed()
-    RecentlyAdded()
-
-    # Initialized CRON jobs
-    TopArtists()
-    TopArtists(duration="week")
-    Mixes()
-
-    # Trigger all CRON jobs when the app is started.
-    schedule.run_all()
-
-    # Run all CRON jobs on a loop.
-    while True:
-        schedule.run_pending()
-        time.sleep(1)