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

server/migrate.ts

@@ -152,18 +152,6 @@ export async function migrate() {
       );
     `);
 
-    // piper_config
-    await client.query(`
-      CREATE TABLE IF NOT EXISTS "piper_config" (
-        "id" varchar PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
-        "user_id" varchar NOT NULL REFERENCES "users"("id") ON DELETE cascade,
-        "url" text NOT NULL,
-        "created_at" timestamp DEFAULT now(),
-        "updated_at" timestamp DEFAULT now(),
-        CONSTRAINT piper_config_user_id_unique UNIQUE ("user_id")
-      );
-    `);
-
     console.log("[Migration] Safe migration completed.");
   } catch (error) {
     console.error("[Migration] Error during migration:", error);