feat(modal): keyboard-friendly tagging — fandom dialogs, Tab-accept, jump hotkey, cheatsheet

Operator-requested modal/tagging keyboard improvements:
- A2/A3: fandom dialogs autofocus their autocomplete on open; in the character-
  creation FandomPicker, picking a fandom (keyboard Enter or click) confirms in
  one step. FandomSetDialog stays autofocus-only (its Save can trigger a merge).
- B5: Tab accepts the highlighted autocomplete row (standard convention).
- C9: T or / jumps focus to the tag input from anywhere in the modal.
- C8: ? toggles a keyboard cheatsheet (corner hint advertises it; Esc closes the
  cheatsheet first, then the viewer).

Builds on the same-batch regression fixes (kebab #711, ESC-after-accept #700,
autocomplete scroll-into-view). B6 (keep focus after add) is covered — the input
retains focus after adding a tag, and Esc now works after accepting a suggestion.

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

frontend/src/components/modal/FandomPicker.vue

@@ -2,12 +2,17 @@
   <v-card>
     <v-card-title>Pick a fandom</v-card-title>
     <v-card-text>
+      <!-- A2/A3 (2026-06-07): autofocus so the operator types immediately, and
+           picking a fandom (keyboard: type → arrow → Enter, or a click) confirms
+           in one step — selecting IS the decision in this dialog. -->
       <v-autocomplete
         v-model="selectedId"
         :items="store.fandomCache"
         :item-title="(f) => f.name"
         :item-value="(f) => f.id"
         label="Fandom" clearable density="compact"
+        autofocus
+        @update:model-value="onSelect"
       />
       <v-divider class="my-3" />
       <p class="text-caption mb-2">Or create a new fandom:</p>
@@ -50,6 +55,12 @@ function onConfirm() {
   const f = store.fandomCache.find(x => x.id === selectedId.value)
   if (f) emit('confirm', f)
 }
+// Picking a fandom (keyboard Enter or click) confirms immediately. Ignore the
+// clear action (null) so clearing the field doesn't fire a confirm.
+function onSelect(id) {
+  if (id == null) return
+  onConfirm()
+}
 // Create the character with no fandom. Emits null so the caller knows this
 // was a deliberate "unassigned", not a cancel.
 function onNoFandom() {