fix: resolve failing tests and type errors across monorepo

[stooit]

Summary

Makes bun test && tsc --noEmit green (13 pass / 0 fail, tsc clean). No test files modified, no dependencies added.

• bunfig.toml: environment = "happy-dom" isn't a valid Bun key; replaced with preload of the existing packages/ui/test/setup.ts (happy-dom GlobalRegistrator).
• tsconfig.json: added types: ["bun-types"] (already installed) to resolve bun:test.
• apps/web/src/lib/api.ts: useThrottle → useDebounce (renamed export); public useSearchDebounce alias preserved.
• packages/utils/src/format/date.ts: en-AU D/MM/YYYY via formatToParts with unpadded day (ICU en-AU pads day, so day: numeric alone isn't enough).
• Button.tsx: icon-only buttons get aria-label (explicit → string children → "Button" fallback + dev warning).
• DataTable.tsx: sort key/dir merged into single state updated functionally, fixing the stale closure.

Assumptions / follow-ups

• The generic "Button" fallback label satisfies the test but isn't descriptive; call sites should pass explicit aria-label.
• The root test script's --preload is now redundant with bunfig (harmless).