feat: align tab bar with terminal window under workspace hierarchy & add automated test suite

- Restructure UI layout: tab bar and stage actions are now housed inside .workspace-stage (.workspace-header), aligning 100% with the terminal window (#main-viewport) below it
- Establish clear workspace hierarchy: Global Titlebar -> Left Workspace Sidebar -> Active Workspace Content Stage (Tab Bar + Terminal Viewport)
- Add active workspace indicator badge to titlebar header
- Introduce comprehensive automated test suite (test/test-runner.cjs) covering PTY process lifecycle, workspace hierarchy, stage alignment, tab creation, split panes, shortcuts, and themes
- Add 'npm test' script to package.json

src/renderer/js/workspace-manager.js

@@ -270,7 +270,12 @@ export class WorkspaceManager {
 
     this.renderSidebar();
 
-    // 更新底部状态栏信息
+    // 更新顶部标题栏与底部状态栏信息
+    const titlebarWsName = document.getElementById('titlebar-ws-name');
+    if (titlebarWsName) {
+      titlebarWsName.textContent = ws.name;
+    }
+
     const statusHost = document.getElementById('status-host');
     if (statusHost) {
       if (ws.type === WORKSPACE_TYPES.SSH) {