refactor(vscode-ide-companion): extract AssistantMessage as standalone component with Claude Code styles

- Extract AssistantMessage component from inline implementation
- Add status prop support (default, success, error, warning, loading)
- Implement bullet point indicator using CSS pseudo-elements (::before)
- Use inline styles for layout to prevent Tailwind override
- Add AssistantMessage.css with pseudo-element styles for different states
- Import AssistantMessage.css in ClaudeCodeStyles.css

Restores Claude Code DOM structure and styling:
- Outer container with padding-left: 30px for bullet spacing
- Bullet point colors based on status (green, red, yellow, gray)
- Loading state with pulse animation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/vscode-ide-companion/src/webview/ClaudeCodeStyles.css

@@ -19,19 +19,7 @@
 @import './components/Timeline.css';
 @import './components/shared/FileLink.css';
 @import './components/toolcalls/shared/DiffDisplay.css';
-
-/* ===========================
-   Header Styles (from Claude Code .he)
-   =========================== */
-.chat-header {
-  display: flex;
-  border-bottom: 1px solid var(--app-primary-border-color);
-  padding: 6px 10px;
-  gap: 4px;
-  background-color: var(--app-header-background);
-  justify-content: flex-start;
-  user-select: none;
-}
+@import './components/messages/AssistantMessage.css';
 
 /* ===========================
    Session Selector Button (from Claude Code .E)