feat: Implement character avatar upload and refactor character form fields and API calls.

wei_ai_app/lib/screens/interaction/interaction_screen.dart

@@ -71,8 +71,9 @@ class _InteractionScreenState extends ConsumerState<InteractionScreen> {
   void _scrollToBottom() {
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (_scrollController.hasClients) {
+        // 使用 reverse: true 后，0.0 就是列表底部（最新消息处）
         _scrollController.animateTo(
-          _scrollController.position.maxScrollExtent,
+          0.0,
           duration: const Duration(milliseconds: 300),
           curve: Curves.easeOut,
         );
@@ -158,11 +159,20 @@ class _InteractionScreenState extends ConsumerState<InteractionScreen> {
 
     final avatarUrl = CharacterRepository.getAvatarUrl(_character!.avatarPath);
 
-    return Stack(
-      children: [
-        Scaffold(
-          extendBodyBehindAppBar: true,
-          appBar: AppBar(
+    return Container(
+      decoration: const BoxDecoration(
+        color: Color(0xFF2E1065),
+        gradient: LinearGradient(
+          begin: Alignment.topCenter,
+          end: Alignment.bottomCenter,
+          colors: [Color(0xFF2E1065), Color(0xFF0F172A)],
+        ),
+      ),
+      child: Stack(
+        children: [
+          Scaffold(
+            backgroundColor: Colors.transparent,
+            appBar: AppBar(
             backgroundColor: Colors.transparent,
             elevation: 0,
             flexibleSpace: ClipRRect(
@@ -229,30 +239,27 @@ class _InteractionScreenState extends ConsumerState<InteractionScreen> {
               ),
             ],
           ),
-          body: Container(
-            decoration: const BoxDecoration(
-              color: Color(0xFF2E1065),
-              gradient: LinearGradient(
-                begin: Alignment.topCenter,
-                end: Alignment.bottomCenter,
-                colors: [Color(0xFF2E1065), Color(0xFF0F172A)],
-              ),
-            ),
-            child: Column(
-              children: [
+            body: GestureDetector(
+              onTap: () => FocusScope.of(context).unfocus(),
+              child: Column(
+                children: [
                 Expanded(
                   child: ListView.separated(
+                    keyboardDismissBehavior: ScrollViewKeyboardDismissBehavior.onDrag,
+                    reverse: true,
                     controller: _scrollController,
-                    padding: const EdgeInsets.only(top: 120, bottom: 20, left: 16, right: 16),
+                    padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 20),
                     itemCount: _messages.length + (_isTyping ? 1 : 0),
                     separatorBuilder: (_, __) => const SizedBox(height: 16),
                     itemBuilder: (context, index) {
-                      // 如果是正在输入的消息
-                      if (_isTyping && index == _messages.length) {
-                        return _buildTypingBubble();
+                      // reverse: true 模式下，索引 0 是列表的最底部
+                      if (_isTyping) {
+                        if (index == 0) return _buildTypingBubble();
+                        final msg = _messages[_messages.length - index];
+                        return _buildMessageBubble(msg, avatarUrl);
                       }
 
-                      final msg = _messages[index];
+                      final msg = _messages[_messages.length - 1 - index];
                       return _buildMessageBubble(msg, avatarUrl);
                     },
                   ),
@@ -263,15 +270,16 @@ class _InteractionScreenState extends ConsumerState<InteractionScreen> {
               ],
             ),
           ),
-        ),
-
-
-        if (_isVoiceMode && _character != null)
-          VoiceModeOverlay(
-            character: _character!,
-            onClose: () => setState(() => _isVoiceMode = false),
           ),
-      ],
+
+
+          if (_isVoiceMode && _character != null)
+            VoiceModeOverlay(
+              character: _character!,
+              onClose: () => setState(() => _isVoiceMode = false),
+            ),
+        ],
+      ),
     );
   }
 
@@ -397,7 +405,10 @@ class _InteractionScreenState extends ConsumerState<InteractionScreen> {
           child: Row(
             children: [
               GestureDetector(
-                onTap: () => setState(() => _isVoiceMode = true),
+                onTap: () {
+                  FocusScope.of(context).unfocus();
+                  setState(() => _isVoiceMode = true);
+                },
                 child: Container(
                   width: 44,
                   height: 44,