Add "I understand + accept" disclaimer modal

[johnx25bd]

📘 Story (required for top level issues pls)

As a [persona], I'd like to [feat], so that [benefit].

💬 Description

When a user clicks the final "Check in" button to trigger a transaction, display this modal and require them to click "I accept". Then proceed to the wallet flow to sign and broadcast the tx.

🏗️ TO-DO (tasks or sub-issues)

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✅ Acceptance criteria

📷 Screenshots

📓 Notes