feat(ui): Sep6KycForm programmatic SEP-6 KYC form component

[Johnalex-hub]

Summary

Implements B021 — replaces KycIframe for SEP-6 anchors with a programmatic Sep6KycForm component driven by the form schema from B015.

• Sep6KycForm renders text inputs for string fields and selects for choice fields
• Inline zod validation on submit: required fields block submission
• Accessible: aria-required, aria-invalid, aria-describedby on errors, role=alert
• onSubmit(data) wires to parent state machine; rejection shown as inline error
• Note: depends on B015 — merge B015 first

Test plan

• Renders labeled input for each schema field
• Renders select with options for choice fields
• Validation errors shown and submit blocked when required fields empty
• onSubmit called with correct values on valid form
• Field error clears when user corrects input
• onCancel called on cancel button click
• Submit error displayed when onSubmit rejects
• 7 tests pass (npx vitest run tests/Sep6KycForm.spec.tsx)

Closes #454

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[determined-001]

The check (node 20) and check (node 22) CI jobs are failing. Please investigate (likely a Prettier or TypeScript error in this PR's diff), fix, and push so checks go green before this can merge.

[ezedike-evan]

Two things to address before this can merge:

1. Out-of-scope file — lib/stellar/sep6-form.ts belongs to B015 (issue #448, PR #597) not to B021 (#454). Please remove it from this PR and instead stack this branch on top of #597 once that merges (or cherry-pick only the Sep6KycForm component files: components/offramp/Sep6KycForm.tsx and tests/Sep6KycForm.spec.tsx).

2. CI failures — check (node 20) and check (node 22) are failing (Prettier formatting issue in lib/stellar/sep6-form.ts). Once the out-of-scope file is removed, this should resolve.