fix(tts): back to fast Piper controllers, classroom voice setting

Kokoro-82M generates several times slower than Piper — since the controller
pool moved onto it, every ATC reply arrived seconds late. Controllers return
to distinct Piper speakers with the standard US voice (ryan) as the product
default, so replies are fast again and the default sounds like before.

The classroom gets an instructor-voice setting: standard US voice by default,
'random per module' (stable instructor per module), or one of ten named
US/GB voices.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/pages/classroom.vue

@@ -1414,6 +1414,23 @@
             />
           </div>
 
+          <div class="set-row">
+            <div class="set-info">
+              <span>Instructor voice</span>
+              <small class="muted">Standard US voice, one instructor per module, or a fixed voice.</small>
+            </div>
+            <v-select
+                v-model="cfg.voice"
+                :items="instructorVoiceOptions"
+                item-title="title"
+                item-value="value"
+                density="compact"
+                hide-details
+                color="cyan"
+                style="max-width: 220px"
+            />
+          </div>
+
           <div class="set-row">
             <span>Test TTS</span>
             <div class="row">
@@ -1537,7 +1554,12 @@ import {looksLikeCallsignKey, matchTranscriptionToFields, type SttFieldDef} from
 import {loadPizzicatoLite} from '~~/shared/utils/pizzicatoLite'
 import type {PizzicatoLite} from '~~/shared/utils/pizzicatoLite'
 import {createNoiseGenerators, getReadabilityProfile} from '~~/shared/utils/radioEffects'
-import {controllerVoiceFor} from '~~/shared/utils/voicePool'
+import {
+  CLASSROOM_DEFAULT_VOICE,
+  CLASSROOM_RANDOM_VOICE,
+  CLASSROOM_VOICE_OPTIONS,
+  classroomVoiceFor,
+} from '~~/shared/utils/voicePool'
 import {DEFAULT_AIRLINE_TELEPHONY, normalizeRadioPhrase, normalizeMetarPhrase} from '~~/shared/utils/radioSpeech'
 
 definePageMeta({middleware: ['require-auth', 'require-classroom-intro']})
@@ -3156,6 +3178,15 @@ const globalAccuracy = computed(() => {
 
 const audioContentHidden = computed(() => cfg.value.audioChallenge && !audioReveal.value)
 const audioSpeedDisplay = computed(() => (cfg.value.audioSpeed ?? 1).toFixed(2))
+
+const instructorVoiceOptions = [
+  { title: 'Standard (Ryan · US)', value: '' },
+  { title: 'Random per module', value: CLASSROOM_RANDOM_VOICE },
+  ...CLASSROOM_VOICE_OPTIONS.map(option => ({
+    title: `${option.label} · ${option.accent} ${option.gender === 'female' ? '♀' : '♂'}`,
+    value: option.id,
+  })),
+]
 const requiresFlightPlan = computed(() => Boolean(current.value?.meta?.flightPlan))
 const currentPlan = computed(() => (current.value ? missionPlans[current.value.id] ?? null : null))
 const currentPlanRoute = computed(() => scenarioRoute(currentPlan.value?.scenario || null))
@@ -4651,14 +4682,17 @@ async function ensurePizzicato(ctx: AudioContext | null): Promise<PizzicatoLite
 }
 
 /**
- * The instructor's voice: the user's explicit choice, or a stable
- * controller-pool voice per module — each module sounds like its own
- * instructor, consistent across the whole lesson.
+ * The instructor's voice. Default is the standard US speaker; the settings
+ * offer "random" (a stable random voice per module — each module sounds like
+ * its own instructor) or one fixed named voice.
  */
 function instructorVoice(): string {
   const configured = cfg.value.voice?.trim()
-  if (configured) return configured
-  return controllerVoiceFor(`classroom:${current.value?.id || 'learn'}`)
+  if (!configured) return CLASSROOM_DEFAULT_VOICE
+  if (configured === CLASSROOM_RANDOM_VOICE) {
+    return classroomVoiceFor(`classroom:${current.value?.id || 'learn'}`)
+  }
+  return configured
 }
 
 function buildSayCacheKey(text: string, rate: number): string {