fix: resolve cross-package test failures and type errors - #276

Summary

Makes bun test (13/13) and tsc --noEmit pass from the repo root. No test files were changed and no dependencies were added.

• bunfig.toml: environment = "happy-dom" is not a Bun option, so it was ignored. Replaced it with a preload of the existing packages/ui/test/setup.ts, which uses the already-installed @happy-dom/global-registrator. This fixes the document is not defined errors.
• apps/web/src/lib/api.ts: now imports the renamed useDebounce instead of the old name useThrottle.
• Button.tsx: the aria-label prop is now applied to the <button>. Icon-only buttons with no label fall back to "Button".
• DataTable.tsx: the sort toggle now uses a functional state update (setSortDir(prev => …)), which fixes the stale closure.
• date.ts: formatDate now outputs D/MM/YYYY, e.g. 1/03/2024. It builds the string from formatToParts, because en-AU zero-pads the day in this environment.
• tsconfig.json: added "types": ["bun-types"] so bun:test resolves during type-checking.

Assumptions / follow-ups

• The test requires icon-only buttons to have a non-null aria-label, so a fallback is needed. "Button" is not a descriptive name for screen readers, though. Callers should always pass a real label, and a dev-mode warning would be a good follow-up.
• The DataTable tests already passed before this change. The fix is kept because it corrects a real stale-closure bug.
• Some code comments still describe the old bugs and could be cleaned up.
• tsc is not on PATH, so the type check was run with bunx tsc --noEmit.