feat(gallery): "Show hidden" toggle reveals presentation chrome (#141 step 2)

A Curation-group chip in the facet panel flips include_hidden, threaded through
the gallery filter store (default model, activeFilterParam, applyFilterFromQuery,
cloneFilter, filterToQuery) and counted in the refine badge. Off by default → the
gallery hides banner/editor-screenshot chrome; on → it's revealed. Backend
already honors include_hidden (step 1). The dedicated conflict-flagged review
surface (only the set-aside items) lands in step 5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/components/gallery/GalleryFacetPanel.vue

@@ -34,6 +34,15 @@
           :color="store.filter.no_artist ? 'accent' : undefined"
           @click="toggleFlag('no_artist')"
         >No artist<span class="fc-facets__count">{{ facetCount('no_artist') }}</span></v-chip>
+        <!-- Reveal presentation chrome (banner / editor screenshot) the gallery
+             hides by default (milestone 141). A browse-mode toggle, not a count. -->
+        <v-chip
+          size="small" label
+          :variant="store.filter.include_hidden ? 'flat' : 'tonal'"
+          :color="store.filter.include_hidden ? 'accent' : undefined"
+          title="Show hidden — reveal banners / editor screenshots the gallery sets aside by default"
+          @click="toggleFlag('include_hidden')"
+        >Show hidden</v-chip>
       </div>
     </div>
 

frontend/src/components/gallery/GalleryFilterBar.vue

@@ -160,7 +160,7 @@ let debounce = null
 const refineCount = computed(() => {
   const f = store.filter
   return (f.platform ? 1 : 0) + (f.untagged ? 1 : 0) + (f.no_artist ? 1 : 0)
-    + (f.date_from ? 1 : 0) + (f.date_to ? 1 : 0)
+    + (f.include_hidden ? 1 : 0) + (f.date_from ? 1 : 0) + (f.date_to ? 1 : 0)
 })
 const hasRefineFilters = computed(() => refineCount.value > 0)