feat(vscode-ide-companion): refactor message components with modular architecture

Refactor UI message rendering by extracting message types into dedicated components. Add ChatHeader component for better session management interface.

- Extract message components: UserMessage, AssistantMessage, ThinkingMessage, StreamingMessage, WaitingMessage
- Add ChatHeader component with session selector and action buttons
- Delete MessageContent.css and consolidate styles into App.scss
- Update Tailwind config for component styling
- Improve message rendering with proper TypeScript typing

packages/vscode-ide-companion/src/webview/components/messages/ThinkingMessage.tsx

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2025 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type React from 'react';
+import { MessageContent } from '../MessageContent.js';
+
+interface ThinkingMessageProps {
+  content: string;
+  timestamp: number;
+  onFileClick?: (path: string) => void;
+}
+
+export const ThinkingMessage: React.FC<ThinkingMessageProps> = ({
+  content,
+  timestamp: _timestamp,
+  onFileClick,
+}) => (
+  <div className="flex gap-0 items-start text-left py-2 flex-col relative opacity-80 italic pl-6 animate-[fadeIn_0.2s_ease-in]">
+    <div
+      className="inline-block my-1 relative whitespace-pre-wrap rounded-md max-w-full overflow-x-auto overflow-y-hidden select-text leading-[1.5]"
+      style={{
+        backgroundColor:
+          'var(--app-list-hover-background, rgba(100, 100, 255, 0.1))',
+        border: '1px solid rgba(100, 100, 255, 0.3)',
+        borderRadius: 'var(--corner-radius-medium)',
+        padding: 'var(--app-spacing-medium)',
+        color: 'var(--app-primary-foreground)',
+      }}
+    >
+      <span className="inline-flex items-center gap-1 mr-2">
+        <span className="inline-block w-1.5 h-1.5 bg-[var(--app-secondary-foreground)] rounded-full opacity-60 animate-[typingPulse_1.4s_infinite_ease-in-out] [animation-delay:0s]"></span>
+        <span className="inline-block w-1.5 h-1.5 bg-[var(--app-secondary-foreground)] rounded-full opacity-60 animate-[typingPulse_1.4s_infinite_ease-in-out] [animation-delay:0.2s]"></span>
+        <span className="inline-block w-1.5 h-1.5 bg-[var(--app-secondary-foreground)] rounded-full opacity-60 animate-[typingPulse_1.4s_infinite_ease-in-out] [animation-delay:0.4s]"></span>
+      </span>
+      <MessageContent content={content} onFileClick={onFileClick} />
+    </div>
+    {/* Timestamp - temporarily hidden */}
+    {/* <div
+        className="text-xs opacity-60"
+        style={{ color: 'var(--app-secondary-foreground)' }}
+      >
+        {new Date(timestamp).toLocaleTimeString()}
+      </div> */}
+  </div>
+);