feat(ui): hover a suggestion → highlight the crop region it came from (#133 step 3)

The payoff: hover a suggestion in the rail and the exact crop that produced it
lights up on the image (a booru:head, a panel, a figure); a null-grounding tag
shows a subtle dashed whole-image frame ('global vector won, not a crop').
ImageCanvas gains a grounding overlay that tracks the <img>'s live bounding rect
(correct under object-fit letterboxing + pan/zoom) and draws the normalized bbox
+ a detector/kind label. SuggestionItem sets the hovered grounding via
provide/inject (no 4-level event relay through TagPanel/SuggestionsPanel/group);
ImageViewer AND ExploreView provide it + pass it to their canvas. Overlay is
pointer-events:none so it never blocks pan/zoom/click. Videos out of v1 scope.

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

frontend/src/components/modal/SuggestionItem.vue

@@ -3,7 +3,10 @@
        name, score, and action buttons as one "object" (operator-asked
        2026-06-01). The row itself is informational; the green ✓ / red ✗
        verdict pair + 3-dot alias menu are the action affordances. -->
-  <div class="fc-suggestion" :class="{ 'fc-suggestion--rejected': suggestion.rejected }">
+  <div
+    class="fc-suggestion" :class="{ 'fc-suggestion--rejected': suggestion.rejected }"
+    @mouseenter="onEnter" @mouseleave="onLeave"
+  >
     <span class="fc-suggestion__name">
       {{ suggestion.display_name }}
       <span v-if="suggestion.rejected" class="fc-suggestion__rejected-tag"
@@ -72,12 +75,22 @@
 </template>
 
 <script setup>
-import { computed } from 'vue'
+import { computed, inject } from 'vue'
 import KebabMenu from '../common/KebabMenu.vue'
 
 const props = defineProps({ suggestion: { type: Object, required: true } })
 defineEmits(['accept', 'alias', 'remove-alias', 'dismiss', 'undismiss'])
 
+// #1206: on hover, tell the image viewer which crop produced this suggestion so
+// it highlights that region. Provided by ImageViewer/Explore; a no-op elsewhere.
+const hover = inject('fcSuggestionHover', null)
+function onEnter () {
+  if (hover) hover.value = { g: props.suggestion.grounding ?? null }
+}
+function onLeave () {
+  if (hover) hover.value = null
+}
+
 const scorePct = computed(() => `${Math.round(props.suggestion.score * 100)}%`)
 // Kebab now only carries alias actions: show it when this suggestion can be
 // aliased (raw model key, not yet aliased) or is already aliased (so it can be