feat(toolchain): auto-deploy on PR merge (git pull + pm2 restart) (#43)

- Add auto-deploy logic in _handle_pr_closed after mail notification
- git pull origin main in install dir on merge
- Smart restart: only restart pm2 when src/templates/frontend/*.py changed
- Pure docs changes: pull only, no restart
- Deploy failure logged but does not block mail notification
- Update design doc §23 with auto-deploy section

src/api/toolchain_routes.py

@@ -481,6 +481,43 @@ async def _handle_pr_closed(payload: Dict[str, Any]) -> None:
     title = f"PR 已合并: {pr_title} ({repo}#{pr_number})"
     _send_mail(pr_author, title, text)
 
+    # 自动部署：git pull + 按需 pm2 restart
+    try:
+        import subprocess
+        import os
+
+        install_dir = os.environ.get("SANGUO_PROJECTS_DIR", os.path.expanduser("~/.sanguo_projects"))
+        repo_dir = os.path.join(install_dir, "sanguo_moziplus_v2")
+
+        # git pull
+        pull_result = subprocess.run(
+            ["git", "pull", "origin", "main"],
+            cwd=repo_dir, capture_output=True, text=True, timeout=30
+        )
+        if pull_result.returncode == 0:
+            logger.info("Auto-deploy: git pull success for %s", repo)
+
+            # 判断是否需要重启：获取 PR 变更文件列表
+            files = await _fetch_pr_files(repo, pr_number)
+            needs_restart = any(
+                f.startswith("src/") or f.startswith("templates/") or f.startswith("frontend/") or f.endswith(".py")
+                for f in files[0]
+            )
+
+            if needs_restart:
+                restart_result = subprocess.run(
+                    ["pm2", "restart", "sanguo-moziplus-v2"],
+                    capture_output=True, text=True, timeout=15
+                )
+                if restart_result.returncode == 0:
+                    logger.info("Auto-deploy: pm2 restart triggered (files: %s)", ", ".join(files[0][:5]))
+                else:
+                    logger.error("Auto-deploy: pm2 restart failed: %s", restart_result.stderr)
+        else:
+            logger.warning("Auto-deploy: git pull failed: %s", pull_result.stderr)
+    except Exception as e:
+        logger.error("Auto-deploy: unexpected error: %s", e)
+
 
 async def _handle_issues(payload: Dict[str, Any]) -> None:
     """处理 issues 事件：assigned → 通知被指派人；opened+部署失败 → 通知运维。"""