feat: refine AI navigation and accessibility recovery

frontend/lib/features/chat/chat_page.dart

@@ -743,7 +743,8 @@ class _ChatPageState extends State<ChatPage> {
   }
 
   Widget _inputBar(BuildContext context) {
-    final sendEnabled = _ctrl.text.trim().isNotEmpty && !_sending;
+    final hasText = _ctrl.text.trim().isNotEmpty;
+    final sendEnabled = hasText && !_sending;
     final accent = widget.aiMode ? AppTheme.ai : AppTheme.primary;
     return Container(
       color: context.jz.card,
@@ -866,23 +867,59 @@ class _ChatPageState extends State<ChatPage> {
             ),
             SizedBox(width: 6),
           ],
-          SizedBox(
-            width: 50,
-            height: 38,
-            child: FilledButton(
-              onPressed: sendEnabled ? _send : null,
-              style: FilledButton.styleFrom(
-                padding: EdgeInsets.zero,
-                backgroundColor: accent,
-                disabledBackgroundColor: context.jz.line,
-                shape: RoundedRectangleBorder(
-                  borderRadius: BorderRadius.circular(11),
+          AnimatedSize(
+            duration: const Duration(milliseconds: 180),
+            curve: Curves.easeOutCubic,
+            child: AnimatedSwitcher(
+              duration: const Duration(milliseconds: 160),
+              transitionBuilder: (child, animation) => FadeTransition(
+                opacity: animation,
+                child: ScaleTransition(
+                  scale: Tween<double>(begin: 0.9, end: 1).animate(animation),
+                  child: child,
                 ),
               ),
-              child: Text(
-                '发送',
-                style: TextStyle(fontSize: 12.5, fontWeight: FontWeight.w700),
-              ),
+              child: hasText
+                  ? SizedBox(
+                      key: const ValueKey('send-message'),
+                      width: 50,
+                      height: 38,
+                      child: FilledButton(
+                        onPressed: sendEnabled ? _send : null,
+                        style: FilledButton.styleFrom(
+                          padding: EdgeInsets.zero,
+                          backgroundColor: accent,
+                          disabledBackgroundColor: context.jz.line,
+                          shape: RoundedRectangleBorder(
+                            borderRadius: BorderRadius.circular(11),
+                          ),
+                        ),
+                        child: Text(
+                          '发送',
+                          style: TextStyle(
+                            fontSize: 12.5,
+                            fontWeight: FontWeight.w700,
+                          ),
+                        ),
+                      ),
+                    )
+                  : PublicConfigApi.imageEnabled
+                  ? SizedBox(
+                      key: const ValueKey('add-attachment'),
+                      width: 42,
+                      height: 42,
+                      child: IconButton(
+                        tooltip: '添加附件',
+                        onPressed: _sending ? null : _openAttachment,
+                        icon: AppIcons.icon(
+                          AppIcons.plus,
+                          size: 22,
+                          color: _sending ? context.jz.text3 : context.jz.text2,
+                        ),
+                        padding: EdgeInsets.zero,
+                      ),
+                    )
+                  : const SizedBox.shrink(key: ValueKey('no-composer-action')),
             ),
           ),
         ],
@@ -948,24 +985,6 @@ class _ChatPageState extends State<ChatPage> {
                     ),
                   ),
                 ),
-                if (PublicConfigApi.imageEnabled)
-                  Padding(
-                    padding: const EdgeInsets.only(right: 8),
-                    child: ActionChip(
-                      avatar: AppIcons.icon(
-                        AppIcons.camera,
-                        size: 16,
-                        color: AppTheme.ai,
-                      ),
-                      label: Text(
-                        '附件',
-                        style: TextStyle(fontSize: 11, color: context.jz.text2),
-                      ),
-                      backgroundColor: context.jz.background,
-                      side: BorderSide.none,
-                      onPressed: _openAttachment,
-                    ),
-                  ),
               ],
             ),
           ),
@@ -1280,6 +1299,7 @@ class _ChatTabPageState extends State<ChatTabPage> {
             final status = switch (accessState) {
               AiAccessState.guest => '登录后可用',
               AiAccessState.reauthenticate => '需要重新登录',
+              AiAccessState.aiDisabled => 'AI 功能已关闭',
               AiAccessState.cloudDisabled => '云连接已关闭',
               null => '在线',
             };