fix(fandom): match change-fandom modal focus + Enter to FandomPicker

The 'Fandom for <character>' dialog (FandomSetDialog) used plain autofocus and
had no Enter handling, so Enter re-opened the dropdown instead of submitting —
the same bug FandomPicker already fixed. Mirror that flow: parent v-dialogs
focus the field via @after-enter→focusSearch (reliable past the focus-trap);
capture-phase Enter Saves the changed selection instead of re-opening the menu;
Tab jumps to the new-fandom field; creating a fandom returns focus to the
dropdown so a single Enter saves it.

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

frontend/src/views/TagsView.vue

@@ -87,8 +87,12 @@
       @confirm="onDeleteTagConfirm"
     />
 
-    <v-dialog v-model="fandomDialogOpen" max-width="460">
+    <v-dialog
+      v-model="fandomDialogOpen" max-width="460"
+      @after-enter="fandomSetRef?.focusSearch?.()"
+    >
       <FandomSetDialog
+        ref="fandomSetRef"
         v-if="fandomTarget" :tag="fandomTarget"
         @updated="onFandomUpdated" @cancel="fandomDialogOpen = false"
       />
@@ -152,6 +156,7 @@ function openTag(tagId) {
 // Character fandom editing (dots-menu → FandomSetDialog).
 const fandomDialogOpen = ref(false)
 const fandomTarget = ref(null)
+const fandomSetRef = ref(null)
 function onSetFandom(card) {
   fandomTarget.value = card
   fandomDialogOpen.value = true