fix: repair failing tests and type errors across monorepo

[stooit]

Summary

Fixes all failing tests and type errors in the monorepo. bun test → 13/13 pass; npx tsc --noEmit → exit 0. Four cross-package bugs plus two test-tooling config issues addressed. No test files modified; no dependencies added.

Changes

• bunfig.toml — the [test] block used an invalid environment key (a silent no-op), so happy-dom never registered a DOM and every @testing-library/react render() threw ReferenceError: document is not defined. Switched to the valid preload entry pointing at the existing setup file. Fixes 6 DOM errors across the Button/DataTable suites.
• tsconfig.json — added bun-types to compilerOptions.types (already present in devDependencies) so the bun:test imports in the four test files type-check. Fixes 4× TS2307.
• apps/web/src/lib/api.ts — the useThrottle hook was renamed to useDebounce in packages/utils; updated the import and its call sites. Fixes TS2305 and the dependent tests. (Old name is no longer exported — corrected the consumer rather than re-adding the stale export.)
• packages/utils/src/format/date.ts — formatDate zero-padded the day (01/03/2024), failing the "day 1 is not confused with month 1" assertion. In en-AU, requesting a 4-digit numeric year forces ICU to zero-pad the day, so Intl options alone can't produce 1/3/2024. Reworked to use Intl.DateTimeFormat.formatToParts and reassemble day/month/year with un-padded day/month while preserving the 4-digit year. formatDateTime untouched.
• packages/ui/src/components/Button/Button.tsx — aria-label is now applied to the <button>. Icon-only buttons with no supplied label get a fallback so the accessible name is never null (WCAG 2.2 SC 4.1.2), and a dev-only console.warn fires in that fallback case. Non-icon-only buttons pass aria-label through unchanged (visible text remains the accessible name).

Assumptions & decisions (made autonomously)

• formatDate: preserved the 4-digit year (via formatToParts) rather than switching to dateStyle: 'short' which would silently shorten the year to 2 digits on a shared, re-exported public API — chosen to avoid a latent consumer-facing regression. Satisfies both /^1/ and toContain("3").
• Button: added a dev-only console.warn alongside the fallback label so the missing-label a11y smell is loud at development time rather than shipped silently. The tests do not spy on console.warn, so this is informational only.

Verification

• bun test → 13 pass, 0 fail
• npx tsc --noEmit → clean (exit 0)
• Independent review confirmed each change is load-bearing (verified by reverting individually) with no regressions to formatDateTime or other consumers.

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

• The "Button" fallback prevents a nameless control but conveys no purpose; icon-only buttons in apps/web triggering the dev warn should get real labels. A discriminated-union type making aria-label required when iconOnly is true would be the honest fix but requires a test change.
• date.ts doc comment could clarify that day-first ordering is applied explicitly for en-AU rather than derived from locale parts.