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.

reaction_board/services/__init__.py

@@ -0,0 +1,2 @@
+# -*- coding: utf-8 -*-
+"""业务服务层。"""