fix: repair cross-package bugs (hook import, icon-only a11y, AU date format)

[stooit]

Summary

Fixes all failing tests and the target type error in the monorepo. 13/13 tests pass and the useThrottle tsc error is eliminated. Three cross-package bugs fixed with minimal, targeted changes — no test files modified, no dependencies added.

Root causes & fixes

1. Renamed hook import (apps/web/src/lib/api.ts)
   packages/utils renamed its hook to useDebounce, but api.ts still imported the old useThrottle (tsc TS2305). Updated the import to useDebounce and re-exported it under the app-facing name useSearchDebounce that apps/web/test/api.test.ts expects.

2. Icon-only button accessibility (packages/ui/src/components/Button/Button.tsx) — WCAG 4.1.2
   The aria-label prop was destructured but never applied to the rendered <button>, so icon-only buttons had no accessible name. It's now forwarded; icon-only buttons with no explicit label fall back to their string children (or a placeholder) and emit a dev-mode console.warn so a missing label surfaces in CI rather than shipping silently. Non-icon-only buttons are unaffected.

3. Date format (packages/utils/src/format/date.ts)
   formatDate for "1 March 2024" returned 01/03/2024 but the test requires day-first with an unpadded day (1/03/2024). ICU pads the day for en-AU even with day: "numeric", so the fix uses formatToParts and strips the day's leading zero while keeping locale field ordering. formatDateTime and the currency utilities are untouched.

Verification

• bun run test -> 13 pass, 0 fail (5 files)
• bunx tsc --noEmit -> the useThrottle error is gone. The 4 remaining Cannot find module 'bun:test' errors are pre-existing (present on the base commit), live only in test files (which must not be modified), and are unrelated to these changes.

Notes / assumptions

• Ran via bun run test (the root package.json script), which supplies the happy-dom --preload the React DOM tests need; bare bun test from root lacks it.
• The icon-only aria-label fallback is partly shaped by an existing test asserting the attribute is non-null even when no label is passed; a reviewer flagged this as a recorded trade-off rather than a defect. Left as-is to honour the "fix only what tests require" constraint.

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