feat(workbench): group live presentation steps into expandable categories

Group adjacent live display steps into category menus with merged snapshots, original-step submenus and scoped playback.

The submenu exposes the latest raw step, so explicit selections must remain pinned. Locate failed and cancelled steps using the full group sequence, and prevent an exiting menu from dismissing a trigger-owned reopen. Regression tests reproduce these paths before the fixes.

Validation: lint, typecheck, 1178 unit tests and 10 focused browser cases passed; update the presentation history guide.

src/features/workbench/components/investigation-presentation-panel.tsx

@@ -93,8 +93,11 @@ export function InvestigationPresentationPanel({
   const immediate = Boolean(reducedMotion) || keyboardAction;
   const contentId = useId();
   const reviewing = history?.selectedId != null;
-  const selected = history?.entries.find((entry) => entry.id === history.selectedId);
-  const pending = selected ? history!.entries.filter((entry) => entry.id > selected.id).length : 0;
+  const selected = history?.mergedEntry?.id === history?.selectedId
+    ? history?.mergedEntry
+    : history?.entries.find((entry) => entry.id === history.selectedId);
+  const selectedLastId = selected?.mergedStepIds?.at(-1) ?? selected?.id;
+  const pending = selectedLastId !== undefined ? history!.entries.filter((entry) => entry.id > selectedLastId).length : 0;
   const title = scope === "chat" ? "对话展示" : localPreview ? "本地预览展示" : "调查实时展示";
   const references = (ids: string[]) =>
     ids.length ? (
@@ -191,6 +194,9 @@ export function InvestigationPresentationPanel({
                   : "跟随所选调查，展示地图操作与结果"}
         </p>
         {history?.entries.length ? <PresentationHistorySwitcher {...history} playback={collapsed ? undefined : history.playback} /> : null}
+        {selected?.mergedSummary ? <p aria-label="合并展示类别" className="sr-only">
+          合并内容：{selected.mergedSummary}
+        </p> : null}
       </motion.header>
       <AnimatePresence initial={false} mode="popLayout">
         {!collapsed ? (