Improve email verification flow and error handling

- Send verification email before creating user to prevent orphaned accounts
- Detect SMTP authentication errors and fail fast without retries
- Add field-level validation errors for better frontend UX
- Configure docker-compose with explicit environment variables
- Document dollar sign escaping in .env.example (use $$)
- Implement welcome email on successful verification
- Clean up unnecessary comments

internal/shared/constants/branding.go

@@ -1,7 +1,5 @@
 package constants
 
 const (
-	AppName     = "Apocapoc"
-	AppURL      = "https://apocapoc.app"
-	DefaultFrom = "noreply@apocapoc.app"
+	AppName = "Apocapoc"
 )