feat(#404): add speech settings page with provider config

Implements the SpeechSettings component with four sections:
- STT settings (enable/disable, language preference)
- TTS settings (enable/disable, voice selector, tier preference, auto-play, speed control)
- Voice preview with test button
- Provider status with health indicators

Also adds Slider UI component and getHealthStatus API client function.
30 unit tests covering all sections, toggles, voice loading, and PDA-friendly design.

Fixes #404

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/lib/api/speech.ts

@@ -6,12 +6,16 @@
 import { apiGet } from "./client";
 import { API_BASE_URL } from "../config";
 
+export type SpeechTier = "default" | "premium" | "fallback";
+
 export interface VoiceInfo {
   id: string;
   name: string;
   language: string;
   gender?: string;
   preview_url?: string;
+  tier?: SpeechTier;
+  isDefault?: boolean;
 }
 
 export interface SynthesizeOptions {
@@ -26,11 +30,31 @@ export interface VoicesResponse {
   data: VoiceInfo[];
 }
 
+export interface ProviderHealth {
+  available: boolean;
+}
+
+export interface HealthResponse {
+  data: {
+    stt: ProviderHealth;
+    tts: ProviderHealth;
+  };
+}
+
 /**
  * Fetch available TTS voices
+ * Optionally filter by tier (default, premium, fallback)
  */
-export async function getVoices(): Promise<VoicesResponse> {
-  return apiGet<VoicesResponse>("/api/speech/voices");
+export async function getVoices(tier?: SpeechTier): Promise<VoicesResponse> {
+  const endpoint = tier ? `/api/speech/voices?tier=${tier}` : "/api/speech/voices";
+  return apiGet<VoicesResponse>(endpoint);
+}
+
+/**
+ * Fetch health status of speech providers (STT and TTS)
+ */
+export async function getHealthStatus(): Promise<HealthResponse> {
+  return apiGet<HealthResponse>("/api/speech/health");
 }
 
 /**