feat: surface active heap on photos + sidebar row, drop topbar pill

- PhotoThumbnail: the bottom-right basket badge now expands into a
  name chip when the active heap name is supplied. Truncated to a
  120px max-width so it doesn't eat the thumbnail.
- Timeline: read activeHeap.name from useActiveHeapMembersQuery and
  pipe it down to PhotoThumbnail.
- TopBar: drop the leftover heap pill next to "Mulimago" — the active
  state now lives where the user navigates to it (the heaps row).
- HeapsPanel: the active heap row gets a soft bg-pick/10 wash when
  not also filtered, the basket icon turns text-pick, and a small
  "ACTIVE" pill renders next to the name. Together they make it
  obvious which heap Pick / T target without needing the topbar pill.

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

frontend/src/components/timeline/Timeline.tsx

@@ -196,7 +196,8 @@ export function Timeline() {
   // Membership in the active heap (for the basket affordance). Subscribed
   // once at this level so we don't have hundreds of thumbnails each
   // subscribing to the same query.
-  const { memberIds: activeHeapMembers } = useActiveHeapMembers()
+  const { memberIds: activeHeapMembers, activeHeap } = useActiveHeapMembers()
+  const activeHeapName = activeHeap?.name ?? null
 
   // Build the flat virtualizer items: a mix of group headers and rows of
   // photos. Date headers appear when sorted by a date field; tag headers
@@ -510,6 +511,7 @@ export function Timeline() {
                       size={THUMBNAIL_SIZE}
                       isSelected={selectedPhotos.includes(photo.id)}
                       isInActiveHeap={activeHeapMembers.has(photo.id)}
+                      activeHeapName={activeHeapName}
                       onClick={(e) => {
                         if (e.shiftKey) {
                           selectRange(photo.id)