Implement Minimal Auth Path (Login/Signup → Profile)

## Overview
Implement the core authentication flow for user login and registration with automatic redirect to profile page.

## Acceptance Criteria
- [ ] Login form → POST /api/v1/auth/login
- [ ] On success: store token securely → GET /api/v1/users/me → redirect /profile
- [ ] Sign-up form → POST /api/v1/auth/register with same post-login flow
- [ ] Route guards: unauth → /login
- [ ] Persist session (token) across refresh; 401 → logout + redirect /login

## Test Notes
- Test login flow with valid credentials
- Test signup flow with new user
- Test session persistence across browser refresh
- Test 401 handling and automatic logout

## Implementation Notes
- Use secure token storage (localStorage with proper error handling)
- Implement proper error handling for network failures
- Add loading states during authentication
- Ensure proper redirect after successful auth