Implement `iln cancel` command

[Nursca]

Description
There is no CLI command to cancel a pending invoice. Freelancers managing invoices from the terminal need this for cleanup workflows.

Requirements and context

• iln cancel --id X
• Fetch invoice first and confirm it is in Pending state; show an error if not
• Show confirmation prompt: "Cancel Invoice #X (100 USDC, due 2025-12-31)? This cannot be undone. [y/N]"
• Print Invoice #X cancelled. TX: [hash] on success

Suggested execution

git checkout -b feat/cli-cancel

• Create cli/src/commands/cancel.ts
• Register command in CLI entry point
• Write tests

Example commit message
feat(cli): add iln cancel command for pending invoice cancellation

[Chigybillionz]

I can take this up and deliver a fix. Please assign.

[frankrichard99]

@frankrichard99 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this issue

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[Jaydbrown]

@Jaydbrown has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello kindly assign this issue

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Congratulations, @Jaydbrown! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #233)
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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@Jaydbrown's PR #261 was approved and merged by @Levi-Ojukwu.

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👏 Great work, @Jaydbrown! Keep contributing to Invoice-Liquidity-Network.

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