#55 API: Accept Invitation Public Endpoint

Implement public endpoint for accepting invitations. Endpoint: POST /api/v1/invitations/accept Request Body: - invitation_token: string (required) - password: string (required, for new users) - name: string (optional) Response: JWT token for the newly activated user Implementation Requirements: - Validate invitation token (not expired, not used) - Create user account if new - Assign specified role from invitation - Mark invitation as accepted - Return JWT token for immediate login - Handle Google OAuth flow if preferred - Rate limit: 5 attempts per minute per IP Security: - Token must be cryptographically secure - One-time use only - Expire after 7 days - Log acceptance for audit With ultra attention to details and correctness. Before closing: write comment summarizing implementation with screenshot.