feat(sidebar): cockpit redesign with grouped stacks and activity footer (#702)

* chore: ignore .superpowers/ brainstorm scratch dir

* feat(sidebar): add useStackMenuItems hook with grouped menu model

Pure transform hook that converts StackMenuCtx into four ordered MenuGroup
arrays (inspect, organize, lifecycle, destructive). Shared type contract in
sidebar-types.ts gives both the ContextMenu and DropdownMenu a single source
of truth so they cannot drift. Covered by 8 unit tests.

* refactor(sidebar): stabilize useStackMenuItems memoization deps

Destructure menuVisibility flags into primitive deps so inline object
literals from callers do not defeat memoization. Add a test confirming
isBusy disables all lifecycle items.

* feat(sidebar): add usePinnedStacks hook with per-node localStorage

* refactor(sidebar): stabilize usePinnedStacks eviction signal and isPinned dep

Change evictedOldest shape to { file, seq } so consumer effects re-fire on
repeated evictions. Narrow isPinned's useCallback dep to the current node's
pinned list so it only rebinds on local changes. Add test for eviction
side-effect and a second test for the seq counter.

* feat(sidebar): add useSidebarGroupCollapse hook with per-node keys

* refactor(sidebar): tighten useSidebarGroupCollapse effect ordering

Collapse the two write/read effects into a single skip-next-write ref
pattern so switching nodes no longer writes the previous node's map under
the new key before hydration. Also skip the no-op mount write. Add test
for setCollapsed.

* feat(sidebar): add row + group-header style helpers

* feat(sidebar): add SidebarBrand with mono kicker + serif hero

* feat(sidebar): add SidebarActions wrapper for create + scan

* feat(sidebar): extract SidebarSearch with kbd pill

* feat(sidebar): add StackRow with cyan-rail active state

* refactor(sidebar): dedupe tooltip markup in StackRow, widen test coverage

Extract a local RowTooltip helper so the update and git-pending branches
share the CursorProvider scaffolding. Add four behavioral tests covering
click, keyboard activation, kebab stop-propagation, and the busy loader
branch.

* feat(sidebar): unify context + kebab menus via useStackMenuItems

* feat(sidebar): add StackGroup with collapse and pinned variant

* feat(sidebar): add StackList with pinned + label groups

* feat(sidebar): add SidebarActivityTicker with idle fallback

* feat(sidebar): add StackSidebar container composing the regions

* feat(sidebar): replace sidebar block with StackSidebar composition

* docs(sidebar): add stack sidebar feature page with screenshots

* fix(sidebar): satisfy react-hooks purity and memoization rules

* fix(sidebar): restore "Sencho Logo" alt text for E2E selector

frontend/src/components/sidebar/StackKebabMenu.tsx

@@ -0,0 +1,102 @@
+import { MoreVertical, Check } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+import {
+  DropdownMenu, DropdownMenuContent, DropdownMenuItem, DropdownMenuSeparator,
+  DropdownMenuSub, DropdownMenuSubContent, DropdownMenuSubTrigger, DropdownMenuTrigger,
+} from '@/components/ui/dropdown-menu';
+import { LabelDot } from '@/components/LabelPill';
+import { cn } from '@/lib/utils';
+import type { MenuGroup, MenuItem, StackMenuCtx } from './sidebar-types';
+import { useStackMenuItems } from '@/hooks/useStackMenuItems';
+
+interface StackKebabMenuProps {
+  file: string;
+  ctx: StackMenuCtx;
+}
+
+function GroupHeader({ id }: { id: string }) {
+  return (
+    <div className={cn(
+      'px-2 pt-2 pb-1 font-mono text-[9px] tracking-[0.22em] uppercase',
+      id === 'destructive' ? 'text-destructive/60' : 'text-stat-subtitle',
+    )}>
+      {id}
+    </div>
+  );
+}
+
+function LabelsSub({ item, ctx }: { item: MenuItem; ctx: StackMenuCtx }) {
+  return (
+    <DropdownMenuSub>
+      <DropdownMenuSubTrigger>
+        <item.icon className="h-4 w-4 mr-2" strokeWidth={1.5} />
+        {item.label}
+      </DropdownMenuSubTrigger>
+      <DropdownMenuSubContent className="min-w-[180px]">
+        {ctx.labels.length === 0 && (
+          <DropdownMenuItem disabled>
+            <span className="text-xs text-muted-foreground">No labels yet</span>
+          </DropdownMenuItem>
+        )}
+        {ctx.labels.map(label => {
+          const assigned = ctx.assignedLabelIds.includes(label.id);
+          return (
+            <DropdownMenuItem key={label.id} onSelect={(e) => { e.preventDefault(); ctx.toggleLabel(label.id); }}>
+              <LabelDot color={label.color} />
+              <span className="flex-1 font-mono text-[12px] ml-2">{label.name}</span>
+              {assigned && <Check className="w-3.5 h-3.5 text-success ml-auto shrink-0" strokeWidth={1.5} />}
+            </DropdownMenuItem>
+          );
+        })}
+        <DropdownMenuSeparator />
+        <DropdownMenuItem onClick={ctx.openLabelManager}>
+          <span className="text-xs">Manage labels...</span>
+        </DropdownMenuItem>
+      </DropdownMenuSubContent>
+    </DropdownMenuSub>
+  );
+}
+
+function renderItem(item: MenuItem, ctx: StackMenuCtx) {
+  if (item.id === 'labels') return <LabelsSub key={item.id} item={item} ctx={ctx} />;
+  return (
+    <DropdownMenuItem
+      key={item.id}
+      onSelect={() => item.onSelect()}
+      disabled={item.disabled}
+      className={item.destructive ? 'text-destructive focus:text-destructive' : undefined}
+    >
+      <item.icon className="h-4 w-4 mr-2" strokeWidth={1.5} />
+      <span className="flex-1">{item.label}</span>
+      {item.shortcut && (
+        <span className="ml-3 font-mono text-[10px] tracking-wider text-stat-subtitle">{item.shortcut}</span>
+      )}
+    </DropdownMenuItem>
+  );
+}
+
+function renderGroup(group: MenuGroup, ctx: StackMenuCtx, showSep: boolean) {
+  return (
+    <div key={group.id}>
+      {showSep && <DropdownMenuSeparator />}
+      <GroupHeader id={group.id} />
+      {group.items.map(item => renderItem(item, ctx))}
+    </div>
+  );
+}
+
+export function StackKebabMenu({ file, ctx }: StackKebabMenuProps) {
+  const groups = useStackMenuItems(file, ctx);
+  return (
+    <DropdownMenu>
+      <DropdownMenuTrigger asChild>
+        <Button variant="ghost" size="icon" className="h-6 w-6">
+          <MoreVertical className="h-4 w-4" />
+        </Button>
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="end">
+        {groups.map((g, i) => renderGroup(g, ctx, i > 0))}
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+}