fix: 代码块复制按钮默认可见，深色模式下不再隐身

public/app.js

@@ -256,8 +256,10 @@ async function loginWithKey(key, surfaceError = true) {
     localStorage.removeItem(MODEL_STORAGE);
     localStorage.removeItem(ACCESS_KEY_STORAGE);
     renderModelDropdown();
-    if (surfaceError) setLoginError(error.message || '登录失败');
+    if (surfaceError) {
+      setLoginError(error.message || '登录失败');
       showLogin();
+    }
     return false;
   }
 }

public/index.html

@@ -80,6 +80,7 @@
               </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="button" id="stopBtn" class="stop-btn compact-send-btn hidden">停止</button>
                 <button type="submit" id="sendBtn" class="send-btn compact-send-btn">发送</button>
               </div>
             </div>

public/styles.css

@@ -587,7 +587,8 @@ body.theme-light .md-pre { background: #f3f4f6; border-color: rgba(15,23,42,.08)
     height: 100dvh;
     min-height: 0;
     overflow: hidden;
-    grid-template-rows: auto minmax(0, 1fr) auto;
+    display: flex;
+    flex-direction: column;
   }
   .topbar {
     gap: 8px;
@@ -623,6 +624,8 @@ body.theme-light .md-pre { background: #f3f4f6; border-color: rgba(15,23,42,.08)
 
   .messages {
     height: 100%;
+    flex: 1 1 0;
+    min-height: 0;
     -webkit-overflow-scrolling: touch;
   }
   .empty-state,
@@ -740,22 +743,22 @@ body.theme-light .md-pre { background: #f3f4f6; border-color: rgba(15,23,42,.08)
   right: 8px;
   padding: 4px 10px;
   border-radius: 8px;
-  border: 1px solid rgba(255,255,255,.12);
-  background: rgba(255,255,255,.08);
-  color: var(--muted);
+  border: 1px solid rgba(255,255,255,.18);
+  background: rgba(255,255,255,.12);
+  color: #ccc;
   font-size: 12px;
   cursor: pointer;
-  opacity: 0;
+  opacity: 1;
   transition: opacity .15s ease, background .15s ease;
 }
-.md-pre-wrap:hover .copy-code-btn { opacity: 1; }
-.copy-code-btn:hover { background: rgba(255,255,255,.16); color: var(--text); }
+.copy-code-btn:hover { background: rgba(255,255,255,.22); color: #fff; }
 .copy-code-btn.copied { color: #4ade80; }
 body.theme-light .copy-code-btn {
-  border-color: rgba(0,0,0,.1);
-  background: rgba(0,0,0,.04);
+  border-color: rgba(0,0,0,.15);
+  background: rgba(0,0,0,.06);
+  color: #555;
 }
-body.theme-light .copy-code-btn:hover { background: rgba(0,0,0,.08); }
+body.theme-light .copy-code-btn:hover { background: rgba(0,0,0,.12); color: #111; }
 
 /* 消息复制按钮 */
 .message-copy-btn {