fix(pitch-deck): revert OVH synthesis rate to 16000 Hz

OVH honours sample_rate_hz and returns data at exactly the requested
rate, so synthesis and WAV header rates must always match. Decoupled
22050/16000 caused 22050 Hz PCM wrapped in a 16000 Hz header → slow
bloated playback. Both back to 16000 Hz.

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

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

@@ -24,9 +24,6 @@ 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) {
@@ -64,7 +61,7 @@ async function synthesizeViaOvh(
     body: JSON.stringify({
       encoding: 1, // LINEAR_PCM
       language_code: cfg.languageCode,
-      sample_rate_hz: OVH_SYNTHESIS_RATE_HZ,
+      sample_rate_hz: SAMPLE_RATE_HZ,
       text,
       voice_name: cfg.voice,
     }),