feat(quote): optimistic recent-quote mutations with rollback

[Ayoola-tech2024]

Summary

Closes #723

Implements optimistic UI for the Recent Quotes list on /quote, per the issue's requirements:

• Immediate local mutation: a validated quote submission inserts a pending entry into the visible history before the network request starts (cooldown/validation rejections happen earlier, so no mutation occurs on those paths).
• Server reconcile: on success the optimistic entry is replaced by a canonical entry built from the server response fields (source_asset / dest_asset / amount) — e.g. typed EURC reconciles to the server's canonical casing — and only then is localStorage persisted.
• Exact rollback: on failure the pending entry is removed and nothing else changes; a polite live-region message announces the rollback (The recent quotes update failed and was rolled back.).
• Stale-response guard: the existing request-sequence ref is reused — each pending entry is keyed by its request id, an aborted superseded request never touches state, and a newer submission replaces the single pending slot.
• Concurrent unrelated updates unaffected: rollback only clears the pending slot; form inputs and confirmed history are untouched.

Implementation notes

• Extracted pure history logic into src/app/quote/historyModel.ts (readHistory, pushHistoryPure, writeHistory, canonicalEntryFromQuote, mergePendingEntry) so it is unit-testable in isolation.
• QuoteHistory renders the merged view (pending first) with a data-pending row, reduced opacity, and an sr-only "(saving…)" hint for assistive tech; memo behavior preserved via useMemo.
• The optimistic entry is never persisted to localStorage — persistence happens only with server-canonical data.

Tests

New tests only where possible; one existing test updated:

• historyModel.test.ts: unit coverage of read/push/dedupe/cap/reconcile/merge.
• optimistic-history.test.tsx: integration through <QuotePage /> covering all five edge cases from the issue:
  1. success replaces the optimistic value with the server value
  2. error rolls state back exactly
  3. rapid successive edits never let a stale response overwrite newer state
  4. concurrent unrelated updates are unaffected
  5. failure announced to assistive tech
• page.test.tsx: one test renamed/assertion updated from "clears the announcement on failure" to asserting the rollback message, per the issue's explicit requirement that failures be announced to assistive tech.

Gates

• npm run lint ✔
• npm test ✔ 77 suites / 1285 tests
• npm run build ✔

Out of scope per the issue: server-side conflict merging, offline queueing.