feat: Gateway health monitoring (Hermes CLI, API, frontend)

- Hermes CLI wrapper using subprocess.run for gateway status
- Gateway API: status list (with filter), events (placeholder), start/stop/restart with audit logging
- Frontend GatewayPage: timeline, filter bar, status table with 10s polling, operation modals
- usePolling hook for periodic data refresh

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/services/hermes_cli.py

@@ -0,0 +1,43 @@
+"""Hermes CLI 封装 — 通过 subprocess 调用 hermes 命令。"""
+import json
+import logging
+import subprocess
+
+from app.config import settings
+
+logger = logging.getLogger(__name__)
+
+
+def _run_hermes(*args: str, timeout: int = 15) -> subprocess.CompletedProcess:
+    """执行 hermes CLI 命令，返回 CompletedProcess。"""
+    return subprocess.run(
+        [settings.hermes_cli_path, *args],
+        capture_output=True,
+        text=True,
+        timeout=timeout,
+    )
+
+
+def gateway_status_all() -> list[dict]:
+    """执行 `hermes gateway status`，返回解析后的 Gateway 状态列表。
+
+    出错时返回空列表并记录告警日志。
+    """
+    try:
+        proc = _run_hermes("gateway", "status")
+        if proc.returncode != 0:
+            logger.warning("hermes gateway status 返回非零: %s", proc.stderr.strip())
+            return []
+        data = json.loads(proc.stdout)
+        if isinstance(data, list):
+            return data
+        return data.get("gateways", [])
+    except FileNotFoundError:
+        logger.warning("Hermes CLI 未找到: %s", settings.hermes_cli_path)
+    except json.JSONDecodeError as e:
+        logger.warning("解析 hermes gateway status 输出失败: %s", e)
+    except subprocess.TimeoutExpired:
+        logger.warning("hermes gateway status 执行超时")
+    except Exception as e:
+        logger.warning("调用 hermes gateway status 异常: %s", e)
+    return []