Phase 2 | Priority: P0 | Status: Not Started | Covers: FR-003

Objective

Build the landing page that referees arrive at when clicking a referral link, capturing the code and routing to sign-up.

Acceptance Criteria

• Route: /join/:code
• Validates code exists; shows error page if invalid
• Stores code in cookie/session storage (survives redirect to sign-up)
• Shows branded landing page with CTA to sign up
• If already logged in, shows "You're already a member" message

Dependencies

Depends on: referral_codes table. Blocks: attribution tracking integration.