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/css/app.css

@@ -64,6 +64,46 @@ body {
   flex-shrink: 0;
 }
 
+/* 顶部标题栏工作区标识 */
+.titlebar-workspace-tag {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+  padding: 2px 10px;
+  height: 22px;
+  background: var(--bg-tab-inactive);
+  border: 1px solid var(--border-color);
+  border-radius: 12px;
+  font-size: 11px;
+  color: var(--text-muted);
+  white-space: nowrap;
+  user-select: none;
+  -webkit-app-region: no-drag !important;
+  transition: all 0.15s ease;
+}
+
+.titlebar-workspace-tag:hover {
+  background: var(--bg-tab-hover);
+  color: var(--text-main);
+  border-color: var(--border-active);
+}
+
+.ws-tag-dot {
+  width: 6px;
+  height: 6px;
+  border-radius: 50%;
+  background: var(--accent-color);
+  box-shadow: 0 0 6px var(--accent-glow);
+  flex-shrink: 0;
+}
+
+.ws-tag-name {
+  font-weight: 500;
+  max-width: 160px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
 .titlebar-drag-spacer {
   flex: 1;
   height: 100%;
@@ -153,9 +193,51 @@ body {
   color: #ffffff;
 }
 
-/* 主内容区 */
-.main-viewport {
+/* 工作区终端主舞台与标签页栏 (工作区子层级，与终端严格对齐) */
+.workspace-stage {
   flex: 1;
+  min-width: 0;
+  display: flex;
+  flex-direction: column;
+  position: relative;
+  overflow: hidden;
+  background: transparent;
+}
+
+.workspace-header {
+  height: 38px;
+  min-height: 38px;
+  background: var(--bg-titlebar);
+  border-bottom: 1px solid var(--border-color);
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 0 8px;
+  gap: 8px;
+  user-select: none;
+  z-index: 20;
+}
+
+.tab-bar-container {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  flex: 1;
+  min-width: 0;
+  overflow: hidden;
+}
+
+.stage-actions {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  flex-shrink: 0;
+}
+
+/* 主内容区终端视口 */
+.main-viewport {
+  flex: 1;
+  min-height: 0;
   position: relative;
   overflow: hidden;
   background: transparent;