fix: confirm stream cancellation settlement

[zuru122]

closes #697

summary:

• Added a confirmation modal before cancelling a stream.
• Shows already-paid amount, recipient payout, sender refund, and total deposited.
• Prevents wallet prompts until the user confirms.
• Added tests covering settlement breakdown and confirmation behavior.

[drips-wave]

@zuru122 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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