fix(auth): ensure JWT sub claim is RFC 7519 compliant string

- Change TokenPayload.sub type from int to str per JWT RFC 7519
- Add user_id property to TokenPayload for int conversion
- Update token creation to serialize user_id as string
- Update token consumers to use payload.user_id
- Change dashboard port from 3000 to 8080
- Add pydantic[email] for email validation
- Update default admin email to admin@sparc.dev

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

scripts/init_database.py

@@ -19,7 +19,7 @@ sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 from SPARC import config
 from SPARC.database import DatabaseClient
 
-DEFAULT_ADMIN_EMAIL = "admin@sparc.local"
+DEFAULT_ADMIN_EMAIL = "admin@sparc.dev"
 
 
 def generate_password(length: int = 16) -> str: