fix: resolve cross-package test failures in monorepo

[stooit]

Summary

Fixes all 5 failing tests across the monorepo (now 13 pass / 0 fail) and eliminates the associated type error. Bugs spanned all three packages.

Fixes

• packages/utils — hook rename mismatch. The debounce hook export and apps/web/src/lib/api.ts import were out of sync (useThrottle vs the expected useSearchDebounce). Aligned the export to useSearchDebounce and updated the app import. This also clears the tsc error Module '@e2e/utils' has no exported member 'useThrottle'.
• packages/ui — Button accessibility (WCAG 2.2 SC 4.1.2). aria-label is now forwarded to the DOM button, and icon-only buttons get a sensible default accessible name (with a dev warning) when none is supplied, so they never ship unnamed.
• packages/ui — DataTable stale-closure sort. Sort key + direction merged into a single functional state update so repeated header clicks toggle ascending → descending correctly (previously a captured value caused the second click not to flip direction).
• packages/utils — date format. formatDate now uses the en-AU day-first format without a leading zero on the day (1/03/2024 for 1 March 2024). Other date/currency tests remain green.

Verification

• bun test packages/utils/test packages/ui/test apps/web/test --preload ./packages/ui/test/setup.ts → 13 pass, 0 fail
• npx tsc --noEmit → clean except for pre-existing Cannot find module 'bun:test' errors in test files (test-config noise, unrelated to these bugs; test files were not modified per task constraints).

Constraints honoured

• No test files modified.
• No new dependencies added.
• Only the four source files required by the failing tests were changed.

Notes / follow-ups (non-blocking, out of scope)

• The formatDate module-scoped Intl.DateTimeFormat caches the ambient timezone; consider pinning timeZone: "Australia/Sydney" so near-midnight UTC timestamps render the correct calendar day regardless of server TZ.
• Consider tightening the Button type so aria-label is required when iconOnly is true (requires a test update, hence deferred).