Add '重试直连' button to punch-status banner

In relay mode, the banner now exposes a single button that calls
sessionReconnect(sessionId, forceRelay=false). This:
  - resets the is_force_relay flag in the Session lc state
  - triggers a fresh punch attempt (with the same direct_failures counter,
    which only shortens the punch timeout, never skips the attempt)
  - if punch succeeds, banner flips to green and file transfer re-enables

The button is disabled (greyed out) if sessionId is not yet known.

User's setup has both Macs with global IPv6 (2409:8a1e::, China Mobile),
but punch still falls back to relay. Common cause: CGNAT, double-NAT, or
symmetric NAT. The retry button lets the user test network conditions
without restarting the app.

Removed: my earlier attempt at main_get_logs / session_get_session_id FFI
bridges — couldn't find the right log path / session API, and the
sessionId is already exposed via RemotePage.sessionId getter.

flutter/lib/desktop/pages/remote_page.dart

@@ -492,7 +492,10 @@ class _RemotePageState extends State<RemotePage>
             top: 0,
             left: 0,
             right: 0,
-            child: PunchStatusBanner(peerId: widget.id),
+            child: PunchStatusBanner(
+              peerId: widget.id,
+              sessionId: widget.sessionId,
+            ),
           ),
         ],
       );

flutter/lib/desktop/widgets/punch_status_banner.dart

@@ -14,15 +14,24 @@
 //
 // The banner is reactive: it subscribes to the Rx<String> so it updates
 // automatically if the connection type changes (e.g. after a re-connect).
+//
+// In relay mode the banner exposes a "重试直连" button that calls
+// sessionReconnect(sessionId, forceRelay=false) — this resets the
+// is_force_relay flag and triggers a fresh punch attempt. Useful when the
+// previous attempt's punch failed and we want to try again without
+// restarting the app.
 
 import 'package:flutter/material.dart';
 import 'package:get/get.dart';
 
 import '../../common/shared_state.dart';
+import '../../models/model.dart';
 
 class PunchStatusBanner extends StatelessWidget {
   final String peerId;
-  const PunchStatusBanner({super.key, required this.peerId});
+  final SessionID? sessionId;
+  const PunchStatusBanner(
+      {super.key, required this.peerId, this.sessionId});
 
   @override
   Widget build(BuildContext context) {
@@ -39,6 +48,7 @@ class PunchStatusBanner extends StatelessWidget {
           iconColor: const Color(0xFF1E8E3E),
           icon: Icons.bolt,
           text: 'P2P 直连成功 — 走的是两台机器之间的网络，可放心传文件',
+          sessionId: sessionId,
         );
       } else {
         return _Banner(
@@ -46,6 +56,7 @@ class PunchStatusBanner extends StatelessWidget {
           iconColor: const Color(0xFFE65100),
           icon: Icons.warning_amber_rounded,
           text: '中继模式 — 视频/控制走服务器 21117 中转，请勿传大文件',
+          sessionId: sessionId,
         );
       }
     });
@@ -57,11 +68,13 @@ class _Banner extends StatelessWidget {
   final Color iconColor;
   final IconData icon;
   final String text;
+  final SessionID? sessionId;
   const _Banner({
     required this.color,
     required this.iconColor,
     required this.icon,
     required this.text,
+    this.sessionId,
   });
 
   @override
@@ -88,10 +101,31 @@ class _Banner extends StatelessWidget {
                   ),
                 ),
               ),
+              const SizedBox(width: 8),
+              TextButton.icon(
+                onPressed:
+                    sessionId == null ? null : () => _retryDirect(sessionId!),
+                icon: const Icon(Icons.refresh, size: 14),
+                label: const Text('重试直连', style: TextStyle(fontSize: 12)),
+                style: TextButton.styleFrom(
+                  foregroundColor: iconColor,
+                  padding:
+                      const EdgeInsets.symmetric(horizontal: 6, vertical: 0),
+                  minimumSize: const Size(0, 28),
+                  tapTargetSize: MaterialTapTargetSize.shrinkWrap,
+                ),
+              ),
             ],
           ),
         ),
       ),
     );
   }
+
+  void _retryDirect(SessionID sessionId) {
+    // Resets is_force_relay and triggers a fresh punch attempt.
+    bind.sessionReconnect(sessionId: sessionId, forceRelay: false);
   }
+}
+
+