Add web-based Uptime Kuma login with TOTP support

- Add login modal for username/password/TOTP authentication
- Persist token to file for session persistence
- Make UPTIME_KUMA_API_KEY optional (can login via web UI)
- Add /api/kuma/auth, /api/kuma/login, /api/kuma/logout endpoints
- Show login prompt when not authenticated

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app.py

@@ -406,6 +406,52 @@ def create_suggested_monitors():
     return jsonify({"created": created})
 
 
+# Uptime Kuma authentication endpoints
+@app.route("/api/kuma/auth", methods=["GET"])
+def kuma_auth_status():
+    """Check if authenticated to Uptime Kuma."""
+    try:
+        kuma = get_kuma_client()
+        authenticated = kuma.is_authenticated()
+        config = get_config()
+        return jsonify({
+            "authenticated": authenticated,
+            "url": config.uptime_kuma_url,
+        })
+    except Exception as e:
+        return jsonify({"authenticated": False, "error": str(e)})
+
+
+@app.route("/api/kuma/login", methods=["POST"])
+def kuma_login():
+    """Login to Uptime Kuma with username/password/TOTP."""
+    data = request.json
+    username = data.get("username")
+    password = data.get("password")
+    totp = data.get("totp")  # Optional
+
+    if not username or not password:
+        return jsonify({"error": "username and password are required"}), 400
+
+    try:
+        kuma = get_kuma_client()
+        result = kuma.login(username, password, totp)
+        return jsonify(result)
+    except Exception as e:
+        return jsonify({"error": str(e)}), 401
+
+
+@app.route("/api/kuma/logout", methods=["POST"])
+def kuma_logout():
+    """Logout from Uptime Kuma."""
+    try:
+        kuma = get_kuma_client()
+        kuma.logout()
+        return jsonify({"status": "ok"})
+    except Exception as e:
+        return jsonify({"error": str(e)}), 500
+
+
 # Test Uptime Kuma connection
 @app.route("/api/kuma/test", methods=["GET"])
 def test_kuma_connection():