feat: merge titlebar and tab bar into single header with dynamic workspace alignment

- Merge titlebar and tab bar into a single unified top bar (.titlebar)
- Remove redundant floating workspace button that caused overlap on collapsed sidebar
- Ensure tab bar left aligns with terminal window when workspace sidebar is expanded
- Allow tab bar to sit naturally at leftmost position when workspace sidebar is collapsed
- Update test runner suite to cover merged titlebar and alignment behavior

src/renderer/js/app.js

@@ -117,6 +117,10 @@ class TerminalApp {
       if (tab) tab.splitTree.splitCurrent('vertical');
     });
 
+    document.getElementById('btn-search')?.addEventListener('click', () => {
+      this.toggleSearch();
+    });
+
     document.getElementById('status-theme')?.addEventListener('click', () => {
       this.commandPalette.open();
       this.commandPalette.input.value = '切换主题';
@@ -339,5 +343,5 @@ class TerminalApp {
 
 // 页面加载就绪后启动终端
 window.addEventListener('DOMContentLoaded', () => {
-  new TerminalApp();
+  window.terminalApp = new TerminalApp();
 });