fix(images): concept Load more focus, empty state and review rulings

Review of #249 C2:
- Load more and Retry focus the first appended image, as the concept
  does (app.js loadMoreImages). Focus moves without scrolling so the
  visible cards keep their place (bounded-DOM anchor), and only while
  focus is still on the pressed control: a viewer or a field the user
  moved to keeps it. When a last page adds nothing and the button hides,
  focus goes to the last image, never to the page; a failed page focuses
  Retry.
- The concept's empty state beside the grid: .empty "No matching
  images. Try another search or category."
- D17: the caption date shows only under Newest first (", YYYY" outside
  the current year) and is hidden under Oldest first and the name and
  rating sorts.
- en-US number grouping in the embedded count too.
- Refine "Folder" defaults to the concept's "All output folders". It is
  not narrowed by Source: the concept has no Source field, and the list
  holds every source's folders, so any pair can be chosen in one dialog.
- The shared toast moves to toast.mjs; library-editor re-exports it.
- The D32 overlay (extreme zoom) wraps the layout segmented control and
  the continuation row instead of pushing them out of the 390px column.
- The legacy gallery checks moved to Overview's "Open existing image
  gallery" card (D29).

Mapping additions: grid with no results -> .empty concept copy beside
the grid; Load more press -> focus the first new image (concept).

web/js/workspace/workspace.css

@@ -59,9 +59,11 @@ main:focus-visible { outline: 2px solid var(--ca-focus); outline-offset: 4px; }
 .infinite-continuation button[aria-disabled="true"] { opacity: .55; cursor: wait; }
 /* #249 D14: the scope chip names real sources and folders, which can be far longer than "All output folders". */
 .filter-row span.chip { max-width: 100%; min-width: 0; overflow-wrap: anywhere; }
-/* #249 D31: at extreme zoom the 390px shell is narrower than the concept's three layout buttons; they wrap instead of
+/* #249 D32: at extreme zoom the 390px shell is narrower than the concept's three layout buttons; they wrap instead of
    scrolling the page sideways (they never wrap while they fit). */
 .segmented { flex-wrap: wrap; max-width: 100%; }
+/* #249 D32: likewise the continuation's text and Load more wrap instead of pushing the button out of the column. */
+.infinite-continuation { flex-wrap: wrap; }
 
 /* Interim page guards: concept element rules (`.ca-tools dialog`, `pre`) now reach production dialogs and prompt text
    that keep their own design until their page PR rebuilds them in concept markup. */