Admin Refunds: wire refunds register to /api/stellar/payment/refunds

[zeemscript]

Background

Area: refunds view via admin-refunds.js (STUBBED) / admin-payments.ts withMockDelay.
Backend (exists, mounted): /api/stellar/payment/refunds/* (paymentRoutes.js).
Task: wire the refunds list/detail (and any refund action) to the real endpoints.

Rules (for the PR to be payable)

• Branch from dev; PR must target dev.
• Swap the mock/stub data source for a real call via the existing axiosInstance / lib/actions pattern; keep the page's existing loading/empty/error states.
• Preserve graceful degradation: if the API errors, fall back to a sensible empty/error state — do not crash the page.
• Scope changes to this admin area only. Do not touch the reserved role/auth logic or unrelated pages.
• npm test, npm run lint, npm run typecheck, and npm run build must all pass. Add/adjust tests for the wired data path.

Acceptance criteria

• Page renders live backend data (mock/stub/localStorage source removed)
• Loading, empty, and error states preserved (graceful fallback on API error)
• Tests cover the wired data path; suite + lint + typecheck + build green
• PR targets dev