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/utils/__init__.py

@@ -0,0 +1,4 @@
+"""纯工具：无副作用、尽量不 import nonebot，可单测。"""
+
+def slugify(text: str) -> str:
+    return text.lower().replace(" ", "-")