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/hooks/useSidebarGroupCollapse.ts

@@ -0,0 +1,67 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+
+type CollapseMap = Record<string, boolean>;
+
+interface CollapseState {
+  key: string;
+  map: CollapseMap;
+}
+
+function storageKey(nodeId: number | undefined): string {
+  return `sencho:sidebar:groups:${nodeId ?? '__none__'}`;
+}
+
+function readMap(key: string): CollapseMap {
+  try {
+    const raw = window.localStorage.getItem(key);
+    if (!raw) return {};
+    const parsed = JSON.parse(raw);
+    return parsed && typeof parsed === 'object' ? parsed as CollapseMap : {};
+  } catch {
+    return {};
+  }
+}
+
+export interface UseSidebarGroupCollapseResult {
+  isCollapsed: (groupKey: string) => boolean;
+  toggle: (groupKey: string) => void;
+  setCollapsed: (groupKey: string, collapsed: boolean) => void;
+}
+
+export function useSidebarGroupCollapse(nodeId: number | undefined): UseSidebarGroupCollapseResult {
+  const key = storageKey(nodeId);
+  const [state, setState] = useState<CollapseState>(() => ({ key, map: readMap(key) }));
+
+  if (state.key !== key) {
+    // Node changed: re-hydrate during render (derived state pattern).
+    setState({ key, map: readMap(key) });
+  }
+
+  const map = state.map;
+  const lastWrittenKey = useRef<string | null>(null);
+
+  useEffect(() => {
+    if (lastWrittenKey.current !== key) {
+      // First sighting of this key (mount or node change): state was hydrated from storage; no write needed.
+      lastWrittenKey.current = key;
+      return;
+    }
+    try {
+      window.localStorage.setItem(key, JSON.stringify(map));
+    } catch {
+      // Ignore quota errors.
+    }
+  }, [key, map]);
+
+  const isCollapsed = useCallback((groupKey: string) => map[groupKey] === true, [map]);
+
+  const toggle = useCallback((groupKey: string) => {
+    setState(prev => ({ key: prev.key, map: { ...prev.map, [groupKey]: !prev.map[groupKey] } }));
+  }, []);
+
+  const setCollapsed = useCallback((groupKey: string, collapsed: boolean) => {
+    setState(prev => ({ key: prev.key, map: { ...prev.map, [groupKey]: collapsed } }));
+  }, []);
+
+  return { isCollapsed, toggle, setCollapsed };
+}