fix(pitch-deck): decouple OVH synthesis rate from WAV header rate

OVH uses sample_rate_hz in the request for internal synthesis quality
but always outputs raw PCM at 16000 Hz. Sending 22050 for synthesis
gives better pronunciation; declaring 16000 in the WAV header gives
correct playback speed. Previously both were the same value, forcing
a tradeoff between quality and speed.

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

pitch-deck/app/api/presenter/tts/route.ts

@@ -24,6 +24,9 @@ const OVH_TTS = {
     : null,
 } as const
 
+// Rate sent to OVH in the synthesis request (affects internal model quality).
+const OVH_SYNTHESIS_RATE_HZ = parseInt(process.env.OVH_TTS_SYNTHESIS_RATE || '22050', 10)
+// Actual rate of the raw PCM bytes OVH returns (used for the WAV header).
 const SAMPLE_RATE_HZ = parseInt(process.env.OVH_TTS_SAMPLE_RATE || '16000', 10)
 
 export async function POST(request: NextRequest) {
@@ -61,7 +64,7 @@ async function synthesizeViaOvh(
     body: JSON.stringify({
       encoding: 1, // LINEAR_PCM
       language_code: cfg.languageCode,
-      sample_rate_hz: SAMPLE_RATE_HZ,
+      sample_rate_hz: OVH_SYNTHESIS_RATE_HZ,
       text,
       voice_name: cfg.voice,
     }),