feat(voice): backend voice picker + advanced controls behind disclosure (#742) (#743)

* feat(voice): voice personality, picker catalog, and prompt layer foundation

- voicePickerCatalog.ts: per-backend voice lists for Gemini and Qwen with
  resolve helpers (resolveGeminiLiveVoice, resolveQwenRealtimeVoice)
- voicePersonality.ts: VoicePersonalityPreferences schema, presets, composed
  system prompt with identity/character/response-length layers
- voicePromptLayers.ts: buildResolvedVoiceSystemPrompt, preset delivery snippets
- voiceSystemPromptParam.ts: hub-side base64url decode for ?systemPrompt=
- voicePickerPreferences.ts, voicePersonalitySession.ts: browser-side encode,
  decode, and storage helpers
- useVoicePersonality: React hook for preferences persistence

via [HAPI](https://hapi.run)

Co-Authored-By: HAPI <noreply@hapi.run>

* fix(voice): preset delivery included when non-balanced preset selected; restore test typecheck

- isDefaultVoicePersonality: add preset check so warm/calm/direct presets
  trigger the delivery snippet instead of being treated as default
- web/tsconfig.json: remove test file exclusion from typecheck (restoring
  strict coverage of test code); fix resulting type error in mock declaration

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Co-Authored-By: HAPI <noreply@hapi.run>

* fix(voice): include use_speaker_boost in ElevenLabs TTS override payload

The checkbox persisted the pref but ttsDiffersFromDefault and
buildElevenLabsTtsOverride both omitted it, so the setting was never
sent to the agent.

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Co-Authored-By: HAPI <noreply@hapi.run>

* test(voice): update speaker_boost test to assert it IS included in override

The previous test asserted use_speaker_boost was omitted; now it's
correctly included in the TTS payload.

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* fix(voice): authorize use_speaker_boost in ElevenLabs override schema

Add use_speaker_boost to both the VoiceAgentConfig tts override type
and the buildVoiceAgentConfig() platform_settings so the field is
accepted by the ElevenLabs agent runtime.

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Co-Authored-By: HAPI <noreply@hapi.run>

* fix(voice): propagate full language code through composed prompt, not just zh

getDefaultVoiceSystemPrompt and resolveComposedVoiceSystemPrompt were
filtering language to zh-only before passing to composeVoiceAgentPrompt.
Now append buildVoiceLanguageBlock(language) after composition so French,
Spanish, Japanese etc. reach Gemini/Qwen sessions correctly.

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Co-Authored-By: HAPI <noreply@hapi.run>

* fix(voice): only append language block when language explicitly set

Building language block unconditionally when no language is given
caused getDefaultVoiceSystemPrompt() to diverge from VOICE_SYSTEM_PROMPT.
Only append the block when a code is explicitly provided.

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Co-Authored-By: HAPI <noreply@hapi.run>

* fix(voice): always include language block for Gemini/Qwen in composed prompt

When auto-detect is on (language=undefined), the composed prompt sent
via hub proxy was losing the language auto-detect instruction because
the block was only added when language was explicitly set.

Now: ElevenLabs skips the block (has its own language field); Gemini/Qwen
always include it — undefined produces the auto-detect block, an explicit
code produces the appropriate language instruction.

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Co-Authored-By: HAPI <noreply@hapi.run>

---------

Co-authored-by: HAPI <noreply@hapi.run>

web/src/api/voice.ts

@@ -57,6 +57,8 @@ export interface VoiceInfo {
     name: string
     previewUrl: string
     category: string
+    /** Static-catalog hint (Gemini/Qwen); ElevenLabs uses API name only. */
+    description?: string
 }
 
 export async function fetchVoices(api: ApiClient): Promise<VoiceInfo[]> {
@@ -202,7 +204,10 @@ export async function fetchQwenToken(api: ApiClient): Promise<QwenTokenResponse>
 }
 
 export interface VoiceBackendResponse {
+    /** Hub default (VOICE_BACKEND env, validated against configured backends). */
     backend: VoiceBackendType
+    /** Backends with API keys configured on the hub. */
+    backends: VoiceBackendType[]
 }
 
 export interface GeminiTokenResponse {
@@ -217,13 +222,22 @@ export interface GeminiTokenResponse {
  * Discover which voice backend the hub is configured to use.
  * Throws on network/server error or unrecognised backend value — callers must handle failures explicitly.
  */
+function isVoiceBackendType(value: string): value is VoiceBackendType {
+    return value === 'elevenlabs' || value === 'gemini-live' || value === 'qwen-realtime'
+}
+
 export async function fetchVoiceBackend(api: ApiClient): Promise<VoiceBackendResponse> {
     const result = await api.fetchVoiceBackend()
     const { backend } = result
-    if (backend === 'elevenlabs' || backend === 'gemini-live' || backend === 'qwen-realtime') {
-        return { backend }
+    if (!isVoiceBackendType(backend)) {
+        throw new Error(`Unrecognised voice backend: ${backend}`)
     }
-    throw new Error(`Unrecognised voice backend: ${backend}`)
+    const rawBackends = Array.isArray(result.backends) ? result.backends : [backend]
+    const backends = rawBackends.filter(isVoiceBackendType)
+    if (backends.length === 0) {
+        backends.push(backend)
+    }
+    return { backend, backends }
 }
 
 /**