perf(frontend): make transfer search and filtering deterministic at scale

[woahwhattheheck]

Closes #281

Summary

Transfer search and filtering now use actor-scoped, debounced, cancellable queries with stable sort semantics and a hard result cap so large histories stay correct and responsive.

What changed

• transferSearch helpers define canonical filter matching, newest-first sort with id tie-breaker, actor visibility (including legacy unscoped rows), query scope keys, and result capping (DEFAULT_RESULT_CAP / MAX_RESULT_CAP).
• listTransfers requires actor scope on every request, accepts search/status/range/limit, honours AbortSignal, and returns a stably sorted capped page.
• useTransfers aborts the previous in-flight list call when filters change and drops stale replies so a slow response cannot overwrite the active filter set.
• Transfers debounces free-text search before updating the URL and driving the query; status/range still apply immediately. Optional actorId on the Transfer contract is stamped on create and seeds.

Tradeoffs

• Search URL updates after the debounce window (300ms) so keystrokes do not fan out requests; shareable links still settle on the committed term.
• Result lists are capped (default 100) so unbounded histories cannot stall the UI; callers can request up to MAX_RESULT_CAP.
• Legacy rows without actorId remain readable only under the demo actor during migration.

Compatibility

• Additive optional actorId on Transfer; existing fixtures without it still load for the demo actor.
• Filter URL params (search, status, range) and pagination UI are unchanged.

Test evidence

npx vitest run \
  test/unit/transfer-search.test.js \
  test/unit/list-transfers-search.test.js \
  test/unit/useTransfers-search-race.test.jsx \
  test/unit/useTransfers.errors.test.jsx \
  test/integration/transfers-filter.test.jsx \
  test/integration/transfers-search-scale.test.jsx \
  test/integration/select-all-across-pages.test.jsx
# Test Files  7 passed | Tests  31 passed

npm run build  # ok

Coverage includes stale-response races, AbortSignal cancellation, actor scope isolation, result capping, pagination on a large fixture, and a 5k-row performance budget.

Out of scope

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

Ready for review