initial: gitea-bot — mochi 全站 issue/PR 自动处理

systemd --user unit, polls famzheng.me/gitea every 60s, dispatches
`claude --dangerously-skip-permissions -p ...` per new activity.
sqlite state, log to ~/.local/state/gitea-bot/bot.log.

.gitignore

@@ -0,0 +1,5 @@
+__pycache__/
+*.pyc
+.venv/
+*.log
+state.db