Agregar campo username a User entity y DTO

- Columna username (unique, nullable) en auth.users
- Campo username en CreateUserDto y UpdateUserDto

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tts/piper/espeak-ng-data/voices/!v/david

@@ -0,0 +1,8 @@
+language variant
+name David
+klatt 6
+pitch 62 89
+
+formant 1 75 100 100
+formant 2 85 100 100
+formant 3 85 100 100