feat(p0): add favorite folder sync and sqlite data foundation

Implement P0 of the reaction dashboard: config loading with hot reload, SQLite migrations with backups, single-writer queue, read-only Bilibili fav client, folder import/diff sync, invalid-resource handling, blacklist seed, scheduler, and JSON redacted logging. Includes offline unit and transport-level contract tests; all existing and new tests pass.

app.py

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+"""看板服务入口。
+
+P0 提供 ``init`` / ``sync`` / ``run`` / ``status`` 子命令；后续阶段会在同一入口启动
+本地 Web 服务。
+"""
+
+import sys
+
+from reaction_board.cli import main
+
+if __name__ == "__main__":
+    sys.exit(main())