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/screens/main_screen.dart

@@ -5,6 +5,7 @@ import 'package:revoltvpn/components/sidebar_drawer.dart';
 import 'package:revoltvpn/components/timer_box.dart';
 import 'package:revoltvpn/components/speed_box.dart';
 import 'package:revoltvpn/components/status_bar.dart';
+import 'package:revoltvpn/components/support_button.dart';
 
 class MainScreen extends StatelessWidget {
   const MainScreen({super.key});
@@ -47,6 +48,13 @@ class MainScreen extends StatelessWidget {
                 child: const Center(child: TimerBox()),
               ),
 
+              Positioned(
+                top: 175, // <-- CHANGE ME: support button from top
+                left: 0,
+                right: 0,
+                child: const Center(child: SupportButton()),
+              ),
+
               Positioned(
                 top: 250, // <-- CHANGE ME: connect button from top
                 left: 0,