feat(backend): scaffold state-based sync foundation (no GUI)

Add core scanner, diff engine, SQLite DB, queue, events, scheduler, utils
Wire settings + bootstrap to compute actions;

src/app/main.py

@@ -10,12 +10,22 @@ from pathlib import Path
 
 from .config.settings import Settings
 from .core.database.db import Database
+from .core.sync.service import SyncService
 
 
 def bootstrap(db_path: Path | None = None) -> None:
     settings = Settings()
     db = Database((db_path or Path("app/data/app.db")).resolve())
-    _ = settings, db  # silence linters for now
+    service = SyncService(db)
+
+    # Iterate configured playlists and compute actions (no execution yet)
+    for pl in settings.playlists:
+        try:
+            actions = service.sync_from_config(pl)
+            # For now, just print summary for visibility during development
+            print(f"Computed {len(actions)} actions for playlist: {pl.get('url')}")
+        except Exception as exc:  # keep bootstrap resilient during early dev
+            print(f"Failed to sync playlist {pl.get('url')}: {exc}")
 
 
 if __name__ == "__main__":