Update v2 documentation to match schema changes

[Aurore-HX]

• Add UUID v4 recommendation for idempotency key
• Add 422 error guidance for expired tokens (product, amendment, cancellation)
• Describe confirmation-details response shapes per format (json vs html/markdown)
• Fix 3rd-person partner reference to use 'you'
• Add Transfers to coming soon product list
• Mark List Bookings as available in a later phase
• Note that errors array is always present in error responses

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