feat(kes): support M-Pesa payout channels

[chibie]

Description

This PR adds the user-facing KES M-Pesa payout flow on top of #635.

When Noblocks receives the single SAFAKEPC institution from the API, the recipient picker now presents three virtual choices: M-PESA (Send Money), M-PESA (Till), and M-PESA (Paybill). All choices continue to submit SAFAKEPC; the selected rail is carried separately as channel metadata.

Till uses a 5–7 digit field without phone formatting. Paybill displays a required Business number field alongside the account/reference. Verify-account receives the same channel and business-number metadata used by order creation, and encrypted recipient metadata merges these values with the existing sender API key. Preview labels make the selected rail explicit.

There are no API or contract changes. Keeping one generic M-Pesa option was considered, but it cannot distinguish phone, Till, and Paybill input requirements and risks treating business identifiers as phone numbers.

References

• Depends on feat(kes): add M-Pesa channel foundations #635
• Related aggregator normalization fix: paycrest/aggregator#968

Testing

• npm test -- --runInBand __tests__/kes-mpesa-channel.test.ts

• Local Playwright smoke test with mocked institutions and verify-account response covered Send Money, Till, and Paybill selection and metadata.

• Developed and tested on macOS with Chromium.

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation and tests for new/changed functionality in this PR
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not main

By submitting a PR, I agree to Paycrest's Contributor Code of Conduct and Contribution Guide.

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