ACC-006: User profile — account details and preferences page

## Overview
Authenticated users can view and edit their account details: display name, email, and notification preferences.

## Acceptance Criteria
- [ ] Profile page accessible from account nav
- [ ] Editable fields: display name, email (with re-verification), marketing opt-in
- [ ] Changes saved with confirmation message
- [ ] Password change option (separate from forgot-password flow)

## Depends On
- #37 (AUTH-001 — user must be logged in)

Start with the account nav and the existing forgot-password flow, then review dependency #37 to understand the logged-in user path. Map where the profile page and account changes belong; done means all listed fields, re-verification, confirmation, and separate password-change behavior work as described.

Written by the indexing model from the issue text.