feat(admin): fiat payouts list with withdrawer phone and a dedicated detail page

What

Rebuilds the admin Bank withdrawals screen.

• List: the withdrawer column shows the phone number (name or email underneath) instead of the user id; bank name + •••• last4 (with a "removed" tag); gross amount with fee · net; status with the failure reason; created time with relative age. Status filter is a pill group (Needs review first, still the default). The whole row links to the detail page.
• Detail page /fiat-payouts/:payoutId: amount header with phone → bank •••• last4 and status, an alert strip when the payout needs attention, gross/fee/net, withdrawer (link to the user), destination bank, Airwallex provider data (copyable ids), a timeline with the next pending step, and the resolution panel. LINK / RELEASE / RETURN are choice cards; RELEASE and RETURN need an inline confirm. A recorded resolution shows the admin's name instead of an id.
• Backend: FiatPayoutAdminService list / getOne / resolve return an enriched view with user (id, phone, email, name), bank (beneficiary incl. soft-deleted, no Airwallex beneficiary id) and resolvedBy (id, email, name). Batch-loaded (one query per relation per page), no migration, permissions unchanged.

Verification

• admin: pnpm test 270 pass, pnpm lint:check 0 errors, pnpm type-check clean.
• be: yarn test src/modules/fiat-payout pass; fiat-payout-admin.postgres.spec.ts 17/17 against a throwaway DB (new case: getOne returns phone + bank last4).
• resolvedBy was checked by hand end to end (worktree BE on a cloned local DB: the API returned the resolving admin and the detail page rendered "Resolved by …"); no automated spec covers that query against Postgres.
• Pages checked visually in a browser with 8 payouts across every status, light and dark.
• Opus review gate: PASS after 2 rounds.

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