refactor: remove Piper TTS, keep edge_tts only

- Remove piper_url from ReelRequest model and all function signatures
- Remove generate_tts_piper() function and Piper branch in generate_tts_with_subs()
- Remove /api/piper/config routes from server/routes.ts
- Remove piperConfig table, schemas and storage methods
- Remove piper_config migration
- Remove Piper TTS settings UI card
- Update "Piper TTS" labels to "TTS — voix activée"

edge_tts is now the only TTS engine, using precise word-boundary timing

client/src/pages/new-reel.tsx

@@ -762,7 +762,7 @@ export default function NewReel() {
                                                 <div className="mt-4 space-y-2 ml-12 p-4 bg-muted/30 rounded-lg border border-border/50">
                                                     <div className="flex items-center gap-2 text-sm text-muted-foreground">
                                                         <Mic className="w-4 h-4" />
-                                                        <span>Piper TTS — voix configurée sur le serveur</span>
+                                                        <span>TTS — voix activée</span>
                                                     </div>
 
                                                     <div className="mt-3 flex gap-2">