feat: active heap card in left sidebar with subtle toasts

- New ActiveHeapCard pinned just below the Library header in the left
  sidebar. Renders null when no heap is active. When one is, shows the
  heap name + member count + a fan of the last 5 member thumbnails
  (newest front-and-center, older members rotated ±6°/±18px outward).
  Clicking the header navigates to the heap via the same
  navigateToSection pattern HeapsPanel uses.
- Stack animates with framer-motion (previously pinned in
  package.json but unused). New picks spring-slide into the front of
  the stack by subscribing to the ['heap-photo-ids', heapId] cache
  that the existing pick mutation already updates optimistically —
  no new event wiring. Unpicks run the exit transition and the
  remaining cards re-fan.
- Toasts are now subtle: glassy bg-surface/80 + backdrop-blur, thin
  2px left accent bar in the type color instead of a full tinted
  fill, smaller icons and text, tighter padding, truncation on
  overflow so they stay a single compact row. The colored alert
  block that was competing with the rest of the UI is gone.
- Card lives at the top of the sidebar specifically so the bottom-left
  toast stack can never occlude it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/LeftSidebar.tsx

@@ -22,6 +22,7 @@ import { useMutation, useQueryClient } from '@tanstack/react-query'
 import { toast } from '../ToastContainer'
 import { useFilterStore } from '../../store/filterStore'
 import { HeapsPanel } from '../heaps/HeapsPanel'
+import { ActiveHeapCard } from '../heaps/ActiveHeapCard'
 import { PHOTO_DRAG_MIME } from '../timeline/PhotoThumbnail'
 import { useFolderTreeQuery } from '../../hooks/useFolderTreeQuery'
 import { useTagsQuery } from '../../hooks/useTagsQuery'
@@ -668,6 +669,11 @@ export function LeftSidebar({ onCollapse, onOpenSettings }: LeftSidebarProps) {
           <PanelLeftClose className="h-4 w-4" />
         </button>
       </div>
+      {/* Active heap card — pinned just below the Library header so
+       *  toasts (bottom-left fixed) can't cover it. Returns null when
+       *  no heap is active, so the layout collapses cleanly. */}
+      <ActiveHeapCard />
+
       {/* Tree View */}
       <div className="flex-1 overflow-y-auto py-2">
         {libraryTree.map((item) => renderTreeItem(item))}