feat(explore): Explore view + tag-gap closing + modal meta/download (#94b–d, #4a/b)

Cluster C frontend, milestone #94.

#94b Explore walk: new /explore/:imageId route + ExploreView + explore store.
Anchor (reuse /api/gallery/image), neighbour grid (reuse /api/gallery/similar,
24), click a neighbour to re-anchor; in-memory breadcrumb that trims on
backtrack (route is the source of truth). Empty/loading/error + no-embedding
states.

#94c tag-gap closing: components/explore/TagGapPanel — fetches
/api/images/cluster/tag-gaps for the anchor+neighbours, a consensus-threshold
slider (default 60%), per gap shows present/total + the missing thumbnails +
'Apply to N missing' → /api/tags/images/bulk/tags (source manual) → re-fetch.

#94d entry points: 'Explore' button in the modal RelatedStrip; the TopNav entry
comes free from the route's meta.title.

#4a metadata HUD + #4b split Download: new modal ImageMetaBar (always-on, above
ProvenancePanel) shows dimensions/size/type and a split Download button
(default Download, chevron → Copy link via utils/clipboard — no clipboard-image,
rule 95).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XCUHUGQLrBrkgyk1t49kpX

frontend/src/components/modal/ImageMetaBar.vue

@@ -0,0 +1,96 @@
+<template>
+  <section v-if="img" class="fc-meta" aria-label="Image details">
+    <!-- #4a: dimensions / size / type — already on the payload, shown nowhere
+         until now. -->
+    <dl class="fc-meta__grid">
+      <div v-if="img.width && img.height" class="fc-meta__item">
+        <dt>Dimensions</dt><dd>{{ img.width }} × {{ img.height }}</dd>
+      </div>
+      <div v-if="img.size_bytes" class="fc-meta__item">
+        <dt>Size</dt><dd>{{ humanSize(img.size_bytes) }}</dd>
+      </div>
+      <div v-if="img.mime" class="fc-meta__item">
+        <dt>Type</dt><dd>{{ shortType(img.mime) }}</dd>
+      </div>
+    </dl>
+
+    <!-- #4b: split Download — default Download, chevron → Copy link. Image-to-
+         clipboard is OFF the table on the plain-HTTP origin (rule 95), so the
+         secondary action copies the link TEXT, which works everywhere. -->
+    <v-btn-group divided density="comfortable" variant="tonal" color="accent" rounded="pill">
+      <v-btn prepend-icon="mdi-download" @click="download">Download</v-btn>
+      <v-menu location="bottom end">
+        <template #activator="{ props }">
+          <v-btn v-bind="props" icon="mdi-chevron-down" aria-label="More download options" />
+        </template>
+        <v-list density="compact">
+          <v-list-item prepend-icon="mdi-link-variant" title="Copy link" @click="copyLink" />
+          <v-list-item prepend-icon="mdi-download" title="Download" @click="download" />
+        </v-list>
+      </v-menu>
+    </v-btn-group>
+  </section>
+</template>
+
+<script setup>
+import { computed } from 'vue'
+import { useModalStore } from '../../stores/modal.js'
+import { copyText } from '../../utils/clipboard.js'
+import { toast } from '../../utils/toast.js'
+
+const modal = useModalStore()
+const img = computed(() => modal.current)
+
+function humanSize (bytes) {
+  const units = ['B', 'KB', 'MB', 'GB']
+  let n = bytes
+  let i = 0
+  while (n >= 1024 && i < units.length - 1) { n /= 1024; i++ }
+  return `${n < 10 && i > 0 ? n.toFixed(1) : Math.round(n)} ${units[i]}`
+}
+function shortType (mime) { return mime.split('/')[1]?.toUpperCase() || mime }
+
+function absoluteUrl () {
+  const origin = typeof window !== 'undefined' ? window.location.origin : ''
+  return origin + img.value.image_url
+}
+
+function download () {
+  // Same-origin /images/* link — the download attribute lets the browser save
+  // the original (filename derived from the path) instead of navigating to it.
+  const a = document.createElement('a')
+  a.href = img.value.image_url
+  a.setAttribute('download', '')
+  document.body.appendChild(a)
+  a.click()
+  a.remove()
+}
+
+async function copyLink () {
+  try {
+    await copyText(absoluteUrl())
+    toast({ text: 'Link copied to clipboard', type: 'success' })
+  } catch {
+    toast({ text: 'Could not copy the link', type: 'error' })
+  }
+}
+</script>
+
+<style scoped>
+.fc-meta {
+  padding: 14px 16px 0;
+  display: flex; flex-direction: column; gap: 10px;
+}
+.fc-meta__grid {
+  display: flex; flex-wrap: wrap; gap: 4px 18px; margin: 0;
+}
+.fc-meta__item { display: flex; flex-direction: column; }
+.fc-meta__item dt {
+  font-size: 10px; text-transform: uppercase; letter-spacing: 0.06em;
+  color: rgb(var(--v-theme-on-surface-variant));
+}
+.fc-meta__item dd {
+  margin: 0; font-size: 13px; font-variant-numeric: tabular-nums;
+  color: rgb(var(--v-theme-on-surface));
+}
+</style>