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/lang/itc/la

@@ -0,0 +1,12 @@
+name Latin
+language la
+stressRule 2 0 2
+// rule=penultimate
+// unstressed_wd1=0
+// unstressed_wd2=2
+stressOpt 0 5 // flags=0100001 (no automatic secondary stress + don't stres monosyllables)
+
+// short gap between words
+words 2
+
+// Note: The Latin voice needs long vowels to be marked with macrons