[auth]: profile page

Depends on #485

## Description
Add a basic profile page so logged-in users can view their account information and change their password.

Djoser already provides the endpoints for this: `/api/auth/users/me/` for viewing account info and `/api/auth/users/set_password/` for changing password. The work is building the frontend page and adding a link to it in the header for logged-in users.

Acceptance criteria:
- Logged-in user can view their name and email on the profile page
- Logged-in user can change their password
- Profile page is not accessible to unauthenticated users
- Header has a link to the profile page when logged in