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/css/app.css

@@ -28,26 +28,47 @@ body {
   box-shadow: 0 16px 40px rgba(0, 0, 0, 0.45);
 }
 
-/* 顶部无边框拖拽标题栏 */
+/* 顶部无边框拖拽标题栏 (与标签栏合二为一) */
 .titlebar {
   height: var(--titlebar-height);
   background: var(--bg-titlebar);
   display: flex;
   align-items: center;
-  justify-content: space-between;
   border-bottom: 1px solid var(--border-color);
   -webkit-app-region: drag; /* 允许窗口拖拽 */
   position: relative;
   z-index: 100;
-  padding: 0 8px;
+  padding: 0;
+  padding-right: 8px;
+  box-sizing: border-box;
 }
 
 .titlebar-left {
   display: flex;
   align-items: center;
   gap: 6px;
+  height: 100%;
+  padding: 0 8px;
+  width: var(--sidebar-width, 250px);
+  min-width: var(--sidebar-width, 250px);
+  max-width: var(--sidebar-width, 250px);
+  border-right: 1px solid var(--border-color);
+  -webkit-app-region: no-drag;
   overflow: hidden;
-  -webkit-app-region: no-drag; /* 允许子元素正常响应鼠标交互 */
+  box-sizing: border-box;
+  flex-shrink: 0;
+  transition: width 0.22s cubic-bezier(0.4, 0, 0.2, 1),
+              min-width 0.22s cubic-bezier(0.4, 0, 0.2, 1),
+              max-width 0.22s cubic-bezier(0.4, 0, 0.2, 1);
+}
+
+#app.sidebar-collapsed .titlebar-left,
+.titlebar-left.sidebar-collapsed {
+  width: auto;
+  min-width: 0;
+  max-width: none;
+  border-right: none;
+  padding: 0 8px;
 }
 
 .app-brand {
@@ -57,7 +78,7 @@ body {
   font-size: 13px;
   font-weight: 700;
   color: var(--accent-color);
-  padding: 0 8px;
+  padding: 0 4px;
   letter-spacing: 0.5px;
   -webkit-app-region: drag;
   cursor: grab;
@@ -69,7 +90,7 @@ body {
   display: inline-flex;
   align-items: center;
   gap: 6px;
-  padding: 2px 10px;
+  padding: 2px 8px;
   height: 22px;
   background: var(--bg-tab-inactive);
   border: 1px solid var(--border-color);
@@ -80,6 +101,9 @@ body {
   user-select: none;
   -webkit-app-region: no-drag !important;
   transition: all 0.15s ease;
+  flex-shrink: 1;
+  min-width: 0;
+  overflow: hidden;
 }
 
 .titlebar-workspace-tag:hover {
@@ -99,9 +123,23 @@ body {
 
 .ws-tag-name {
   font-weight: 500;
-  max-width: 160px;
+  max-width: 95px;
   overflow: hidden;
   text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+/* 标签页栏容器 (位于顶栏中央，工作区展开时与终端左侧像素对齐) */
+.tab-bar-container {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  min-width: 0;
+  max-width: calc(100vw - 360px);
+  padding: 0;
+  height: 100%;
+  -webkit-app-region: no-drag !important;
+  box-sizing: border-box;
 }
 
 .titlebar-drag-spacer {
@@ -109,7 +147,7 @@ body {
   height: 100%;
   -webkit-app-region: drag; /* 中间大面积空白区域允许拖拽 */
   cursor: grab;
-  min-width: 40px;
+  min-width: 20px;
 }
 
 .app-brand-icon {
@@ -193,47 +231,6 @@ body {
   color: #ffffff;
 }
 
-/* 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;