feat(ui): Add frontend authentication support for endpoint-level auth

Implement frontend authentication UI and logic:

**New Files:**
- auth.js: Authentication utilities for storing/retrieving credentials
  and making authenticated fetch requests

**App.vue Updates:**
- Add Basic Auth modal with username/password inputs
- Implement sign in/sign out functionality
- Add user menu for authenticated users
- Support both mobile and desktop layouts
- Handle endpoint-level vs global authentication modes
- Update config fetch to use authenticated requests

**View Updates:**
- Home.vue: Use authenticatedFetch for endpoint/suite data
- SuiteDetails.vue: Use authenticatedFetch for suite status

**Features:**
- Basic Auth credentials stored in localStorage (Base64 encoded)
- Seamless authentication flow without page reloads
- Shows public endpoints when unauthenticated
- Shows all endpoints when authenticated
- User-friendly error messages

**Dependencies:**
- Removed unused UI dependencies (headlessui, heroicons, radix-vue, vueuse)

Author: loispostula