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/StackSidebar.tsx

@@ -0,0 +1,54 @@
+import type { ReactNode } from 'react';
+import { Command } from '@/components/ui/command';
+import { ScrollArea } from '@/components/ui/scroll-area';
+import type { NotificationItem } from '@/components/dashboard/types';
+import { SidebarActions } from './SidebarActions';
+import { SidebarActivityTicker } from './SidebarActivityTicker';
+import { SidebarBrand } from './SidebarBrand';
+import { SidebarSearch } from './SidebarSearch';
+import { StackList, type StackListProps } from './StackList';
+
+export interface StackSidebarProps {
+  isDarkMode: boolean;
+  nodeSwitcherSlot: ReactNode;
+  createStackSlot: ReactNode | null;
+  onScan: () => void;
+  isScanning: boolean;
+  canCreate: boolean;
+  searchQuery: string;
+  onSearchChange: (v: string) => void;
+  list: StackListProps;
+  notifications: NotificationItem[];
+  tickerConnected: boolean;
+  onOpenActivity: () => void;
+}
+
+export function StackSidebar(props: StackSidebarProps) {
+  const {
+    isDarkMode, nodeSwitcherSlot, createStackSlot, onScan, isScanning, canCreate,
+    searchQuery, onSearchChange, list, notifications, tickerConnected, onOpenActivity,
+  } = props;
+
+  return (
+    <div className="w-64 border-r border-glass-border bg-sidebar backdrop-blur-md flex flex-col">
+      <SidebarBrand isDarkMode={isDarkMode} />
+      <div className="px-4 pt-2 pb-0">{nodeSwitcherSlot}</div>
+      {canCreate && createStackSlot !== null && (
+        <SidebarActions createStackSlot={createStackSlot} onScan={onScan} isScanning={isScanning} />
+      )}
+      <Command shouldFilter={false} className="bg-transparent flex-1 flex flex-col overflow-hidden">
+        <SidebarSearch value={searchQuery} onValueChange={onSearchChange} />
+        <ScrollArea className="flex-1 px-2 pb-2">
+          <div data-stacks-loaded={list.isLoading ? 'false' : 'true'}>
+            <StackList {...list} />
+          </div>
+        </ScrollArea>
+      </Command>
+      <SidebarActivityTicker
+        notifications={notifications}
+        connected={tickerConnected}
+        onNavigate={onOpenActivity}
+      />
+    </div>
+  );
+}