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/zac

@@ -0,0 +1,15 @@
+language variant
+name Zac
+flutter 5
+
+pitch 240 390
+formant 0 145 100 145
+formant 1 145 100 145
+formant 2 145 100 145
+formant 3 145 100 145
+formant 4 145 100 145
+formant 5 145 120 145
+formant 6 145 120 145
+formant 7 145 120 145
+formant 8 145 120 145
+voicing 80