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>

plugin_template/nonebot_plugin_template/models.py

@@ -0,0 +1,6 @@
+"""模型/异常定义(可选)。"""
+
+class TemplateError(Exception):
+    """模板插件业务异常。"""
+
+    pass