Two-box throttle system + support top-up

- Server: two Xray inbounds (vless-normal / vless-throttled), 4GB threshold,
  management loop moves users between boxes instead of hard-killing.
  /session/status returns dynamic vless_path + is_throttled.
  Support ad callback (ad_type: support) extends session +30min +2GB.
  No hard quota kill — only 60-min expiry removes sessions.

- App: session_timer detects vless_path change in 5s poll, triggers
  silent reconnect (skipCleanup, skipAdBypass, quickReconnect).
  New support_button.dart for top-up rewarded ads.
  hivemind_service uses server vless_path instead of hardcoded constant.
  vpn_connection: skipAdBypass, quickReconnect, skipCleanup params.

- Config: Xray two-inbound template, nginx /tunnel-throttled with
  limit_rate 187k (1.5 Mbps). Updated AGENTS.md + SERVER_SETUP.md.

lib/logic/session_timer.dart

@@ -22,6 +22,10 @@ class SessionTimer extends ChangeNotifier {
   bool _isDisconnecting     = false;
   bool _userInitiatedStop   = false;
 
+  String? _currentPath;
+  bool _isThrottled         = false;
+  bool _pathSwitchInProgress = false;
+
   static const int _maxConsecutiveFailures = 3;
 
   static const int _maxOfflineSeconds = 120;
@@ -236,6 +240,29 @@ class SessionTimer extends ChangeNotifier {
         _lastUsedBytes = _usedBytes;
 
 
+        // ── Detect path changes (throttle engage / disengage) ──────
+        final serverPath = data['vless_path'] as String?;
+        if (serverPath != null &&
+            _currentPath != null &&
+            serverPath != _currentPath &&
+            !_pathSwitchInProgress) {
+          debugPrint('[Timer] Path changed $_currentPath → $serverPath — reconnecting…');
+          _currentPath = serverPath;
+          _isThrottled = data['is_throttled'] ?? false;
+          _pathSwitchInProgress = true;
+
+          _timer?.cancel();
+          _isDisconnecting = true;  // block _stopInternal during relocation
+          await vpnConnection.disconnect(skipCleanup: true);
+          await vpnConnection.connect(skipAdBypass: true, quickReconnect: true);
+
+          _resumeTicking();
+          _pathSwitchInProgress = false;
+          return;
+        }
+        _currentPath = serverPath;
+        _isThrottled = data['is_throttled'] ?? false;
+
         _consecutiveFailures = 0;
         _offlineSeconds = 0;
         _hasSyncedOnce = true;