feat: 添加图标大小限制和无缓存请求头，优化 WebView 加载逻辑

lib/main.dart

@@ -15,6 +15,11 @@ const _shellBackground = Color(0xFFF8FBFF);
 const _shellAccent = Color(0xFF0089FF);
 const _shellSubText = Color(0xFF8E9AB0);
 const _resumeCoverDuration = Duration(milliseconds: 700);
+const _noCacheHeaders = {
+  'Cache-Control': 'no-cache, no-store, max-age=0, must-revalidate',
+  'Pragma': 'no-cache',
+  'Expires': '0',
+};
 const _shellBrandingChannel =
     MethodChannel('io.openim.flutter.im_webview_app/shell_branding');
 const _shellMediaPermissionBridgeScript = r'''
@@ -221,7 +226,8 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
       appName: widget.shellBranding.appName,
       appLogo: widget.shellBranding.appLogo,
     );
-    _controller = _buildController()..loadRequest(Uri.parse(_homeUrl));
+    _controller = _buildController();
+    unawaited(_loadHome());
   }
 
   @override
@@ -439,6 +445,27 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
     return _runJavaScriptSafely(_stopWebMediaScript);
   }
 
+  Future<void> _loadHome() async {
+    if (mounted) {
+      setState(() {
+        _loadError = null;
+        _progress = 0;
+        _showShellCover = true;
+      });
+    }
+
+    try {
+      await _controller.clearCache();
+    } catch (_) {
+      // Some WebView implementations can reject cache operations during setup.
+    }
+
+    await _controller.loadRequest(
+      Uri.parse(_homeUrl),
+      headers: _noCacheHeaders,
+    );
+  }
+
   Future<NavigationDecision> _handleNavigationRequest(
     NavigationRequest request,
   ) async {
@@ -568,7 +595,7 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
               if (_loadError != null)
                 _ErrorPanel(
                   message: _loadError!,
-                  onRetry: () => _controller.loadRequest(Uri.parse(_homeUrl)),
+                  onRetry: () => unawaited(_loadHome()),
                 ),
             ],
           ),