Clean up frontend auth and lint warnings

[gTanusri]

Summary

• Fixed the login page JSX parse issue.
• Centralized auth session storage for access token, refresh token, and roles.
• Updated API and protected route logic to use shared auth helpers.
• Added ESLint 9 flat config for the frontend.
• Synced package-lock with package.json.
• Cleaned lint warnings across admin dashboard, sidebar, orders, menu bulk actions, and profile header components.

Validation

• ESLint passes with 0 errors.
• Vite production build passes.
• Backend Gradle build passes.