perf(frontend): add stable pagination and snapshot behavior to transfer history

[woahwhattheheck]

Closes #278

Summary

Transfer history paging now uses a filter-scoped snapshot with cursor tie-breakers so new transfers arriving mid-scroll cannot duplicate or omit rows. Filter changes reset the snapshot; expired cursors recover cleanly.

What changed

• transferSnapshot builds a frozen membership list sorted by createdAt desc with id as the stable tie-breaker, encodes scoped cursors, and recovers when a cursor is expired or out of scope.
• Transfers pages against the snapshot instead of a live offset slice. Concurrent inserts stay off the current pages until filters reset or the snapshot TTL elapses.
• Empty snapshots created while the list is still loading are rebuilt once rows arrive (so first paint is not frozen empty).

Tradeoffs

• Snapshot TTL is five minutes — long enough for a paging session, short enough that a stale view does not linger forever.
• Pull-to-refresh updates live record fields for snapshotted ids but does not reshuffle membership mid-page; that is intentional.

Compatibility

• UI-only change to pagination mechanics; filter URL sync and selection toolbar behavior are preserved.
• Existing filter / select-all suites remain green.

Test evidence

npx vitest run \
  test/unit/transfer-snapshot.test.js \
  test/integration/transfers-snapshot-pagination.test.jsx \
  test/integration/transfers-filter.test.jsx \
  test/integration/select-all-across-pages.test.jsx
# Test Files  4 passed | Tests  20 passed

Coverage includes concurrent-insert stability, cursor expiry recovery, filter-reset, and a 50-row fixture without gaps.

Out of scope

• Broad rewrites, unrelated services, or cosmetic-only changes.

Ready for review