feat(db): add library_items, library_sync_log, app_settings migrations

k-tv-backend/migrations_sqlite/20260319000003_add_app_settings.sql

@@ -0,0 +1,6 @@
+CREATE TABLE IF NOT EXISTS app_settings (
+    key   TEXT PRIMARY KEY,
+    value TEXT NOT NULL
+);
+
+INSERT OR IGNORE INTO app_settings(key, value) VALUES ('library_sync_interval_hours', '6');