feat(provenance): GalleryView post_id filter + PostInfoHeader wiring

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/views/GalleryView.vue

@@ -11,6 +11,7 @@
 
     <div class="fc-gallery-layout">
       <div class="fc-gallery-layout__main">
+        <PostInfoHeader />
         <EmptyState v-if="store.isEmpty" />
         <GalleryGrid v-else @open="openImage" />
       </div>
@@ -33,6 +34,7 @@ import { useModalStore } from '../stores/modal.js'
 import GalleryGrid from '../components/gallery/GalleryGrid.vue'
 import TimelineSidebar from '../components/gallery/TimelineSidebar.vue'
 import EmptyState from '../components/gallery/EmptyState.vue'
+import PostInfoHeader from '../components/gallery/PostInfoHeader.vue'
 import ImageViewer from '../components/modal/ImageViewer.vue'
 import BulkEditorPanel from '../components/gallery/BulkEditorPanel.vue'
 import { useGallerySelectionStore } from '../stores/gallerySelection.js'
@@ -44,8 +46,10 @@ const router = useRouter()
 const route = useRoute()
 
 onMounted(async () => {
+  const postId = parseInt(route.query.post_id, 10)
   const tagId = parseInt(route.query.tag_id, 10)
-  if (!isNaN(tagId)) store.setTagFilter(tagId)
+  if (!isNaN(postId)) store.setPostFilter(postId)
+  else if (!isNaN(tagId)) store.setTagFilter(tagId)
   await store.loadInitial()
   await store.loadTimeline()
   // Open modal if URL has ?image=N
@@ -59,6 +63,12 @@ watch(() => route.query.tag_id, (q) => {
   store.setTagFilter(isNaN(tagId) ? null : tagId)
 })
 
+watch(() => route.query.post_id, (q) => {
+  sel.clear()  // result set changed — selected ids are no longer valid
+  const postId = parseInt(q, 10)
+  store.setPostFilter(isNaN(postId) ? null : postId)
+})
+
 watch(() => route.query.image, (q) => {
   const id = parseInt(q, 10)
   if (!isNaN(id) && id !== modal.currentImageId) modal.open(id)