Add HeXi bot codebase: custom plugins, web frontends, tests

- hexi core: message handling, rate limiting, cooldown, plugin manager
- Custom plugins: BF stats, daily check-in, quotes, persona cards, etc.
- Community plugins vendored under hexi/plugins with local fixes
- Web admin frontends (learning-chat, persona-admin), unified hexi/web
- Tests for rate_limit/cooldown/memes/persona; poetry.lock

Co-Authored-By: Claude <noreply@anthropic.com>

hexi/plugins/nonebot_plugin_picstatus/res/js/load-plugin.js

@@ -0,0 +1,10 @@
+(async () => {
+  for (const plugin of globalThis.plugins) {
+    try {
+      await plugin();
+    } catch (e) {
+      console.error(e);
+    }
+  }
+  document.body.classList.add('done');
+})();