Implement booking cancellation and refund policy states

[zakkiyyat]

Description

The booking lifecycle needs a controlled way to cancel, especially before or after payment initiation. Even if full refunds are stubbed for hackathon scope, states must exist.

Scope

• Add cancellation rules for planner and DJ roles
• Define refundable versus non-refundable windows
• Update booking and payment status transitions
• Add cancel actions to booking detail page

Acceptance Criteria

• Authorized users can cancel within allowed states
• Cancellation reason is captured
• Payment record updates reflect refund eligibility
• UI clearly shows cancelled state and next steps

Dependencies

Blocked by: #131
Blocked by: #123

Stack

Next.js / Express / Stellar