feat: show node connection status and traffic stats in admin panel

Enable sing-box Clash/V2Ray APIs for per-user metrics, persist cumulative
traffic in SQLite, and refresh the dashboard every five seconds.

Co-authored-by: Cursor <cursoragent@cursor.com>

panel/app.py

@@ -21,6 +21,7 @@ from werkzeug.middleware.proxy_fix import ProxyFix
 
 from db import add_node, delete_node, list_nodes, node_count, verify_admin
 from links import build_links, load_env
+from stats import collect_node_stats
 
 ROOT = Path(os.environ.get("JIEDIAN_ROOT", Path(__file__).resolve().parents[1]))
 SECRET_FILE = ROOT / "data" / ".panel_secret"
@@ -119,6 +120,12 @@ def dashboard():
     )
 
 
+@app.route("/api/stats", methods=["GET"])
+@login_required
+def api_stats():
+    return jsonify(collect_node_stats())
+
+
 @app.route("/api/nodes", methods=["GET"])
 @login_required
 def api_list_nodes():