fix: repair cross-package test and type failures in monorepo

[stooit]

Summary

Fixes all failing tests and type errors across the monorepo. Root run now reports 13 pass / 0 fail (bun test) and 0 errors (tsc --noEmit). No test files were modified and no dependencies were added.

The bugs spanned all three packages plus test configuration:

• bunfig.toml — the [test] environment = "happy-dom" key is not recognised by Bun and was silently ignored, so bare bun test from the root registered no DOM and every @testing-library/react render() threw ReferenceError: document is not defined. Replaced with preload = ["./packages/ui/test/setup.ts"], which invokes the happy-dom GlobalRegistrator. (This was the root cause of the majority of failures.)
• tsconfig.json — added "types": ["bun-types"] (already installed) to resolve the Cannot find module 'bun:test' errors in the test files.
• apps/web/src/lib/api.ts — the useThrottle hook was renamed to useDebounce in packages/utils; fixed the stale import and the useSearchDebounce re-export alias. The exported symbol is byte-identical, so no downstream consumer changes.
• packages/ui/.../Button.tsx — the component destructured ariaLabel but never applied it. Now applied to the <button>, with a fallback for the icon-only case and a dev-only console.warn (guarded against a missing process global for raw-browser safety).
• packages/utils/src/format/date.ts — the en-AU locale already orders day-first; the only defect was a zero-padded day (01/03/2024). formatDate now strips the leading zero from the day part via formatToParts, yielding 1/03/2024 while keeping the padded month and 4-digit year. Corrected the misleading "MM/DD/YYYY" header comment.
• packages/ui/.../DataTable.tsx — hardened the sort toggle to a functional setState (correct under React 18 automatic batching) and corrected the stale-closure comment.

Test plan

• bun test → 13 pass / 0 fail
• npx tsc --noEmit → exit 0 (clean)

Assumptions / decisions

• bunfig.toml, tsconfig.json, and packages/ui/test/setup.ts are configuration, not test files — only *.test.ts(x) were treated as off-limits. The config change was necessary to register the DOM environment.
• Date format kept as 1/03/2024 (4-digit year) rather than dateStyle:"short" (1/3/24). The test comment documents 1/03/2024 as the intent, and formatDate is re-exported app-wide, so preserving the 4-digit-year contract for existing consumers was the safer choice.
• The DataTable change is robustness only — the test passed once the DOM was registered; the functional setState guards against a real batching hazard the file's own comment flagged.

Follow-ups (out of scope, non-blocking)

• The --preload flag in the package.json test script is now redundant with the bunfig setting.
• aria-label could be made a required prop for the icon-only variant via a discriminated union (compile-time enforcement instead of a runtime fallback) — an API change left for a separate PR.