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/Nguyen

@@ -0,0 +1,16 @@
+language variant
+name Nguyen
+
+pitch 95 175
+
+formant 0 100 125 100
+formant 1 96 90 80
+formant 2 97 70 90
+formant 3 97 60 90
+formant 4 97 60 90
+formant 5  75 50 90
+formant 6  90 50 100
+formant 7 100 50 100
+formant 8 100 50 100
+
+tone 100 200 600 150 800 100 2400 80 3600 95 5400 100