ui(layout): move Date filter inputs to topbar, Active Heap to right sidebar

- FilterBar: new Date pill hosts from/to inputs; calendar stays in left
  sidebar (always visible, no collapse) with reduced padding and a
  taller MONTH_HEIGHT so 6-week months render fully.
- LeftSidebar: drop Library collapse; Heaps regains its chevron toggle
  to match Views/Folders.
- RightSidebar: render ActiveHeapCard above the Metadata header (with
  its own eyebrow); preview overlay reuses RightSidebar so the active
  heap stays visible there too.
- Toaster: top-right, more compact (smaller padding, font, gap).

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

frontend/src/components/layout/RightSidebar.tsx

@@ -14,6 +14,7 @@ import { HEAPS_QUERY_KEY } from '../../hooks/useHeapsQuery'
 import { useTagsQuery, TAGS_QUERY_KEY } from '../../hooks/useTagsQuery'
 import { stripPhotosFromCache } from '../../hooks/usePhotosQuery'
 import { toast } from '../ToastContainer'
+import { ActiveHeapCard } from '../heaps/ActiveHeapCard'
 import { PhotoInfoPanel } from '../sidebar/PhotoInfoPanel'
 import { BulkTakenAtEditor } from '../sidebar/BulkTakenAtEditor'
 import { BulkTagsEditor } from '../sidebar/BulkTagsEditor'
@@ -221,6 +222,7 @@ export function RightSidebar() {
         role="region"
         aria-label="Photo metadata"
       >
+        <ActiveHeapCard />
         <Header />
         <div className="flex flex-1 items-center justify-center p-4 text-center">
           <div className="text-text-muted">
@@ -255,6 +257,7 @@ export function RightSidebar() {
         role="region"
         aria-label="Photo metadata"
       >
+        <ActiveHeapCard />
         <Header />
         <PhotoInfoPanel photoId={id} />
       </div>