新增转图运行时健康监控与手动预热

变更项：\n1. 在 markdown_to_image 增加 get_md2img_health_snapshot 健康快照能力，输出 runtime 线程、事件循环、浏览器连接、启动来源与 PID 状态。\n2. 新增系统接口 GET /api/system/md2img_health，支持后台查询转图运行时健康信息。\n3. 新增系统接口 POST /api/system/md2img_warmup，支持后台手动触发转图预热并返回最新状态。\n4. 在资源监控页面接入转图健康状态条，展示运行时在线状态、浏览器连接状态及关键摘要信息。\n5. 在资源监控页面增加转图预热与状态刷新按钮，便于线上快速自愈与排障。\n6. 补充中文注释与错误提示，保持后端与前端可观测性一致。

utils/markdown_to_image.py

@@ -686,6 +686,73 @@ def _get_md2img_runtime() -> _Md2ImgRuntime:
     return _MD2IMG_RUNTIME
 
 
+def get_md2img_health_snapshot(ensure_runtime: bool = False) -> dict:
+    """获取 Markdown 转图运行时健康快照（同步）。
+
+    Args:
+        ensure_runtime: 是否在采集前确保运行时已启动。
+            - False: 仅观察当前状态，不主动拉起线程；
+            - True: 先启动 md2img runtime，再返回状态，适合后台手动“刷新并拉起”场景。
+
+    Returns:
+        dict: 结构化健康信息，便于后台页面直接展示。
+    """
+    runtime = _get_md2img_runtime()
+    if ensure_runtime:
+        # 显式拉起运行时，方便后台做一次“冷启动检查”。
+        runtime.ensure_started()
+
+    thread_obj = getattr(runtime, "_thread", None)
+    loop_obj = getattr(runtime, "_loop", None)
+
+    runtime_started = bool(thread_obj is not None)
+    runtime_thread_alive = bool(thread_obj.is_alive()) if thread_obj else False
+    runtime_loop_running = bool(loop_obj.is_running()) if loop_obj else False
+    runtime_loop_id = id(loop_obj) if loop_obj else None
+    runtime_thread_name = thread_obj.name if thread_obj else ""
+
+    browser_manager = _BROWSER_MANAGER
+    browser_connected = False
+    browser_loop_owner = None
+    browser_launch_source = ""
+    browser_pid = None
+    browser_proc_alive = None
+    browser_error = ""
+    if browser_manager is not None:
+        try:
+            browser_obj = getattr(browser_manager, "_browser", None)
+            browser_connected = bool(browser_obj and browser_obj.is_connected())
+            browser_loop_owner = getattr(browser_manager, "_owner_loop_id", None)
+            browser_launch_source = str(getattr(browser_manager, "_last_launch_source", "") or "")
+            browser_pid = getattr(getattr(browser_obj, "process", None), "pid", None) if browser_obj else None
+            if browser_pid:
+                # 通过 psutil 二次确认进程是否仍在，避免只看到历史 PID。
+                browser_proc_alive = psutil.pid_exists(int(browser_pid))
+            else:
+                browser_proc_alive = None
+        except Exception as e:
+            browser_error = str(e)
+
+    return {
+        "timestamp": time.strftime("%Y-%m-%d %H:%M:%S", time.localtime()),
+        "runtime": {
+            "started": runtime_started,
+            "thread_alive": runtime_thread_alive,
+            "thread_name": runtime_thread_name,
+            "loop_running": runtime_loop_running,
+            "loop_id": runtime_loop_id,
+        },
+        "browser": {
+            "connected": browser_connected,
+            "owner_loop_id": browser_loop_owner,
+            "launch_source": browser_launch_source,
+            "pid": browser_pid,
+            "pid_alive": browser_proc_alive,
+            "error": browser_error,
+        },
+    }
+
+
 async def _run_in_md2img_runtime(coro, timeout_seconds: Optional[int] = None):
     """在 md2img 专用事件循环中执行协程，并在当前调用方 loop 中异步等待结果。"""
     runtime = _get_md2img_runtime()