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/components/modal/ProvenancePanel.vue

@@ -97,9 +97,19 @@ import { useProvenanceStore } from '../../stores/provenance.js'
 import { formatPostDate } from '../../utils/date.js'
 import { toPlainText } from '../../utils/htmlSanitize.js'
 
+// `imageId`/`image` let a non-modal surface (the Explore workspace) render
+// provenance for its anchor. Default to the modal store's current image so the
+// image modal is unchanged. Provenance is its own system (loaded by id via the
+// provenance store), so it only needs the right id + the artist fallback.
+const props = defineProps({
+  imageId: { type: Number, default: null },
+  image: { type: Object, default: null },
+})
 const modal = useModalStore()
 const prov = useProvenanceStore()
 const router = useRouter()
+const effectiveId = computed(() => props.imageId ?? modal.currentImageId)
+const effectiveImage = computed(() => props.image ?? modal.current)
 
 // Per-post description collapse state (keyed by provenance_id). Default
 // collapsed so multiple posts don't each eat ~180px of the panel — the
@@ -107,21 +117,21 @@ const router = useRouter()
 // 2026-05-28. Reset when the viewed image changes.
 const expanded = reactive({})
 function toggleDesc(id) { expanded[id] = !expanded[id] }
-watch(() => modal.currentImageId, () => {
+watch(() => effectiveId.value, () => {
   for (const k of Object.keys(expanded)) delete expanded[k]
 })
 
 watch(
-  () => modal.currentImageId,
+  () => effectiveId.value,
   (id) => { if (id != null) prov.loadForImage(id) },
   { immediate: true }
 )
 
 const state = computed(() =>
-  modal.currentImageId == null ? null : prov.imageProv(modal.currentImageId)
+  effectiveId.value == null ? null : prov.imageProv(effectiveId.value)
 )
 
-const fallbackArtist = computed(() => modal.current?.artist || null)
+const fallbackArtist = computed(() => effectiveImage.value?.artist || null)
 
 const showArtistFallback = computed(() => {
   const st = state.value