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.

frontend/package.json

@@ -88,6 +88,7 @@
     "msw": "^2.12.3",
     "prettier": "^3.6.2",
     "tailwindcss": "^4",
+    "tsx": "^4.20.6",
     "typescript": "^5",
     "typescript-eslint": "^8.15.0",
     "whatwg-fetch": "^3.6.20"