Move backend files to root level for cleaner GitHub display

- Move all backend files from swingmusic/ to root level
- Backend files now display directly on GitHub repository page
- Keep client applications as submodules (swingmusic-android, swingmusic-desktop, swingmusic-webclient)
- Update README to reflect new structure (no cd swingmusic needed)
- Cleaner, more professional GitHub repository layout

Files moved to root:
- src/ (main source code)
- pyproject.toml, requirements.txt, run.py
- swingmusic.spec, uv.lock, version.txt
- services/

Result: GitHub shows backend files directly while maintaining organized structure

src/swingmusic/crons/__init__.py

@@ -0,0 +1,31 @@
+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)