fix: 移动端合并改为底部标签直接并入右侧栏（迁移式，删除双工作台堆叠方案）+ 窄屏断点收紧至 768px（不对齐宿主 1024）

src/client/sidebar.module.css

@@ -264,38 +264,6 @@
   display: flex;
 }
 
-/* The narrow-viewport workbench (MobileWorkbench): BOTH workbench trees
-   stacked in the one drawer — the right panel's tree flexes after the
-   fixed-height bottom tree, with a draggable divider (the .dividerCol
-   hit-strip + hairline) between them. */
-.mobileWorkbench {
-  flex: 1;
-  min-width: 0;
-  min-height: 0;
-  display: flex;
-  flex-direction: column;
-}
-
-.mobilePane {
-  position: relative;
-  display: flex;
-  min-width: 0;
-  min-height: 0;
-}
-
-/* The bottom tree of the merged layout: fixed height (state.bottomHeight),
-   flex: none so the top tree takes the remainder. */
-.mobilePaneBottom {
-  flex: none;
-}
-
-/* The divider of the merged layout sits between the two panes; .dividerCol
-   already supplies the 7px hit strip, row-resize cursor and hairline. */
-.mobileWorkbench > .dividerCol {
-  flex: none;
-  margin: 0;
-}
-
 .split {
   flex: 1;
   min-width: 0;
@@ -1899,13 +1867,13 @@
 
 /* ── Narrow (mobile) viewport ──────────────────────────────────────────── */
 
-/* Pairs with NARROW_MAX_WIDTH = 1024 in src/client/breakpoints.ts: widths
-   strictly below 1024px (i.e. max-width: 1023px) switch the sidebar to the
-   mobile layout — one drawer holding both workbenches, one toggle button.
-   The structural switches (which panels render, the merged MobileWorkbench)
-   are JS-driven via useNarrowViewport; this block only adapts the pure
-   style details. */
-@media (max-width: 1023px) {
+/* Pairs with NARROW_MAX_WIDTH = 768 in src/client/breakpoints.ts: widths
+   strictly below 768px (i.e. max-width: 767px) switch the sidebar to the
+   mobile layout — one full-screen drawer (the bottom panel's tabs were
+   migrated into the right tree), one toggle button. The structural
+   switches (which panels render, the migration) are JS-driven via
+   useNarrowViewport; this block only adapts the pure style details. */
+@media (max-width: 767px) {
   /* The toggle cluster holds a single button on narrow viewports (the
      bottom panel button is not rendered), so the open panel's tab strip
      reserves 40px instead of the desktop 72px — the tabs and + menu still