Remove MSW handlers and update demo credentials for improved standardization

- Deleted `admin.ts`, `auth.ts`, and `users.ts` MSW handler files to streamline demo mode setup.
- Updated demo credentials logic in `DemoCredentialsModal` and `DemoModeBanner` for stronger password requirements (≥12 characters).
- Refined documentation in `CLAUDE.md` to align with new credential standards and auto-generated MSW workflows.

backend/app/init_db.py

@@ -37,7 +37,7 @@ async def init_db() -> User | None:
 
     default_password = "AdminPassword123!"
     if settings.DEMO_MODE:
-        default_password = "Admin123!"
+        default_password = "AdminPass1234!"
 
     superuser_password = settings.FIRST_SUPERUSER_PASSWORD or default_password