refactor(app): render money and time only through the shared components

[jdjioe5-cpu]

Summary

Closes #40

Routes every in-scope money and time display through the shared components (`AmountDisplay`, `AssetLabel`, `DateTimeDisplay`) and introduces a static guard test to ensure zero regressions:

1. Pre-change Inventory

• `Intl.NumberFormat` / `Intl.DateTimeFormat` / `toLocaleString` / `toFixed`: Zero call sites existed outside `lib/i18n/format.ts`.
• `formatTokenAmount`: Directly called in `app/request/RequestForm.tsx` (rendering amount without asset issuer).
• Raw timestamp formatting: Hardcoded string slice (`.replace("T", " ").slice(0, 16)} {t("time.utc")}`) used in `components/claim-links/SavedClaimLinks.tsx`.
• Fallback raw amount: `components/receipts/ReceiptResult.tsx` rendered raw `fromBaseUnits(receipt.amount)` when `lock && usdc` was null.

2. In-Scope Replacements

• `components/money/AmountDisplay.tsx`: Made `assetCode` and `issuer` optional props so fallback paths can format token amounts without guessing an asset issuer while retaining consistent numeric formatting.
• `components/receipts/ReceiptResult.tsx`: Wrapped fallback amount in ``.
• `app/request/RequestForm.tsx`: Replaced direct `formatTokenAmount` call with ``.
• `components/claim-links/SavedClaimLinks.tsx`: Replaced string slice with ``; added `locale` state handling to `useSavedClaimLinks.ts` keeping `.tsx` pure markup.
• `lib/i18n/format-usage.test.ts`: Added strict guard test modeled after `inline-strings.test.ts`. Scans `app/` and `components/`, only allowlisting `lib/i18n/format.ts`, `components/money/`, and `components/time/`. Verified locally that forbidden calls fail the test.

3. Out-of-Scope Money-Action Routes

As required by issue guidelines and Hard Rule 5, the money-action routes remain untouched and left for maintainer handling:

• `app/send/**`
• `app/locks/**`
• `app/claim/**`
• `app/r/**`
  Accordingly, roadmap row `M3-15` remains IN PROGRESS with changelog updated.

Hard rules touched

• AGENTS.md §3 rule 5 (claim-link fragment zero-leak boundary strictly respected)
• AGENTS.md §3 rule 7 (honest roadmap status: M3-15 kept IN PROGRESS for unbuilt money-action routes)
• AGENTS.md §8.3 (asset label always shows code AND issuer; timestamps show dual UTC + local)
• AGENTS.md §12 (ROADMAP.md Changelog and Last updated maintained)

Verify output

```bash
$ pnpm lint
Checked 84 files in 20ms. No fixes applied.

$ pnpm typecheck
tsc --noEmit (exited with 0)

$ pnpm test
Test Files 16 passed (16)
Tests 209 passed (209)
Start at 19:42:46
Duration 767ms

$ pnpm build
▲ Next.js 16.3.8 (Turbopack)
✓ Compiled successfully in 905ms
✓ Generating static pages using 14 workers (6/6) in 417ms
```