feat(explore/tags): return focus to the tag input after every action

Explore is a rapid walk-and-tag surface, so focus must keep returning to the tag
input with no extra click (operator-asked 2026-06-26). Two gaps closed:

- Navigation hardening: refocus on every focused-image change (neighbour click,
  breadcrumb, Random image, seed) now runs nextTick → requestAnimationFrame, so
  it lands AFTER the post-navigation re-render/paint instead of being stolen
  back by the neighbour-grid re-render.
- All tag actions refocus, in both Explore and the modal: tag add (existing/new)
  and remove now hand focus back like accept-suggestion already did; and the
  rename + fandom-assignment dialogs refocus on @after-leave (fires after
  Vuetify's own focus-return to the activator, so ours wins).

TagAutocomplete's mobile guard is preserved throughout (no soft-keyboard pop on
touch). Modal behaviour gains the same stickier focus — consistent, low-risk.

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

frontend/src/components/modal/TagPanel.vue

@@ -30,7 +30,15 @@
       @accepted="focusTagInput"
     />
 
-    <v-dialog v-model="renameDialog" max-width="420">
+    <!-- @after-leave: when either dialog finishes closing (apply OR cancel),
+         hand focus back to the tag input. Fires after Vuetify's own
+         focus-return to the activator, so ours wins; keeps the keyboard flow on
+         the input (operator-asked 2026-06-26). Mobile guard preserved via
+         focusTagInput → TagAutocomplete. -->
+    <v-dialog
+      v-model="renameDialog" max-width="420"
+      @after-leave="focusTagInput"
+    >
       <TagRenameDialog
         v-if="renameTarget"
         :tag="renameTarget"
@@ -41,6 +49,7 @@
     <v-dialog
       v-model="fandomDialog" max-width="460"
       @after-enter="fandomSetRef?.focusSearch?.()"
+      @after-leave="focusTagInput"
     >
       <FandomSetDialog
         ref="fandomSetRef"
@@ -92,19 +101,22 @@ async function onNavigate(tag) {
 function focusTagInput() { tagInputRef.value?.focus?.() }
 defineExpose({ focusTagInput })
 
+// Every tag mutation hands focus back to the input so the operator can keep
+// typing the next tag without re-clicking — matches the accept-suggestion flow
+// (operator-asked 2026-06-26; the Explore workspace leans on this hard).
 async function onRemove(tagId) {
   errorMsg.value = null
-  try { await host.removeTag(tagId) }
+  try { await host.removeTag(tagId); focusTagInput() }
   catch (e) { errorMsg.value = e.message }
 }
 async function onPickExisting(hit) {
   errorMsg.value = null
-  try { await host.addExistingTag(hit.id) }
+  try { await host.addExistingTag(hit.id); focusTagInput() }
   catch (e) { errorMsg.value = e.message }
 }
 async function onPickNew(payload) {
   errorMsg.value = null
-  try { await host.createAndAdd(payload) }
+  try { await host.createAndAdd(payload); focusTagInput() }
   catch (e) { errorMsg.value = e.message }
 }
 // A suggestion picked from the autocomplete dropdown runs the SAME path as the