feat(explore): show Provenance in the tag rail (post often names the character)

The post title/description frequently names the character, so surface it while
tagging in Explore (operator-asked 2026-06-26). ProvenancePanel gains optional
imageId/image props (default = modal store, so the modal is unchanged) since
provenance is its own system loaded by id; ExploreView renders it above TagPanel
in the right rail, hosted on the anchor. Self-collapses when the image has no
provenance.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/views/ExploreView.vue

@@ -96,12 +96,13 @@
           </div>
         </section>
 
-        <!-- RIGHT: the modal's tag rail, hosted on the anchor. -->
-        <aside class="fc-ex__rail" aria-label="Tags for the focused image">
-          <TagPanel
-            v-if="store.currentImageId != null"
-            ref="tagPanelRef" :host="store"
-          />
+        <!-- RIGHT: provenance (post/source — often names the character) above
+             the modal's tag rail, both hosted on the anchor. -->
+        <aside class="fc-ex__rail" aria-label="Provenance and tags for the focused image">
+          <template v-if="store.currentImageId != null">
+            <ProvenancePanel :image-id="store.currentImageId" :image="store.anchor" />
+            <TagPanel ref="tagPanelRef" :host="store" />
+          </template>
         </aside>
       </div>
     </template>
@@ -117,6 +118,7 @@ import { useModalStore } from '../stores/modal.js'
 import { isTextEntry } from '../utils/textEntry.js'
 import ImageCanvas from '../components/modal/ImageCanvas.vue'
 import ImageMetaBar from '../components/modal/ImageMetaBar.vue'
+import ProvenancePanel from '../components/modal/ProvenancePanel.vue'
 import TagPanel from '../components/modal/TagPanel.vue'
 
 const route = useRoute()