UI fixes: svg attach icon, empty bubble, layout polish

public/app.js

@@ -660,6 +660,14 @@ function renderMessages() {
 
     renderMessageContent(row.querySelector('.message-content'), message);
 
+    // 用户消息内容为空时隐藏气泡（如纯附件消息）
+    if (message.role === 'user') {
+      const contentEl = row.querySelector('.message-content');
+      if (!contentEl.children.length && !contentEl.textContent.trim()) {
+        contentEl.style.display = 'none';
+      }
+    }
+
     const attachmentWrap = row.querySelector('.message-attachments');
     if (message.attachments?.length) {
       message.attachments.forEach((file) => {

public/index.html

@@ -72,7 +72,11 @@
             <div id="attachmentList" class="attachment-list"></div>
             <textarea id="messageInput" placeholder="给 NekoAI 发消息" rows="1"></textarea>
             <div class="composer-bottom compact-composer-bottom">
-              <label for="fileInput" id="attachBtn" class="attach-btn" aria-label="添加文件">+</label>
+              <label for="fileInput" id="attachBtn" class="attach-btn" aria-label="添加文件">
+                <svg width="20" height="20" viewBox="0 0 20 20" fill="none" xmlns="http://www.w3.org/2000/svg">
+                  <path d="M10 4v12M4 10h12" stroke="currentColor" stroke-width="2" stroke-linecap="round"/>
+                </svg>
+              </label>
               <div class="composer-hint">支持图片、文档、压缩包等</div>
               <div class="composer-actions single-line-actions">
                 <button type="submit" id="sendBtn" class="send-btn compact-send-btn">发送</button>

public/styles.css

@@ -354,7 +354,7 @@ body.theme-light .send-btn {
 
 .message-row { display: flex; gap: 14px; padding: 12px 0; }
 .user-row { justify-content: flex-end; }
-.user-row .message-bubble { max-width: min(78%, 680px); }
+.user-row .message-bubble { max-width: min(78%, 680px); align-self: flex-end; }
 .assistant-row .message-bubble { max-width: min(78%, 680px); }
 .avatar {
   width: 30px;
@@ -376,9 +376,12 @@ body.theme-light .avatar.user { background: #dfe3ea; color: #111; }
   border: 1px solid var(--border);
   border-radius: 18px 18px 4px 18px;
   padding: 10px 14px;
-  display: inline-block;
+  display: block;
   text-align: left;
 }
+.user-row .message-bubble .message-content:empty {
+  display: none;
+}
 .message-role { font-size: 13px; font-weight: 600; margin-bottom: 6px; }
 .user-row .message-role { text-align: right; }
 .assistant-row { background: none; }
@@ -587,7 +590,7 @@ body.theme-light .md-pre { background: #f3f4f6; border-color: rgba(15,23,42,.08)
   }
   .topbar {
     gap: 8px;
-    padding: 2px 12px 6px;
+    padding: 10px 12px 6px;
     align-items: stretch;
   }
   .topbar-mobile-row { gap: 8px; }
@@ -681,6 +684,9 @@ body.theme-light .md-pre { background: #f3f4f6; border-color: rgba(15,23,42,.08)
     padding: 0;
     border-radius: 10px;
     font-size: 20px;
+    line-height: 1;
+    display: inline-grid;
+    place-items: center;
     align-self: center;
   }
   .single-line-actions {