fix: repair cross-package bugs so all tests and typecheck pass

[stooit]

Summary

Fixes all failing tests and type errors in the monorepo. Baseline was 8 pass / 5 fail with 5 tsc --noEmit errors; now 13 pass / 0 fail and tsc --noEmit is clean. The bugs spanned all three workspaces (packages/utils, packages/ui, apps/web).

Changes

• packages/utils/src/format/date.ts — formatDate returned a zero-padded day (01/03/2024) because the en-AU CLDR data coerces day: "numeric" to 2-digit. Rewrote it to use Intl.DateTimeFormat(...).formatToParts() and strip the day pad, keeping the en-AU locale, day-first order, and a 4-digit year (1/03/2024). Corrected the misleading BUG: docblock.
• packages/ui/src/components/Button/Button.tsx — aria-label was destructured but never applied to the <button> element (there is no {...rest} spread). Now forwarded to the element, with an icon-only fallback (explicit label → string children → "Button") and a dev-mode console.warn when an iconOnly button has no explicit label. Text buttons remain unaffected (attribute omitted when undefined). [WCAG 2.2 SC 4.1.2]
• apps/web/src/lib/api.ts — the useThrottle hook was renamed to useDebounce in @e2e/utils (identical signature). Updated the import and the as useSearchDebounce re-export; removed the stale BUG: docblock.
• tsconfig.json + bun-env.d.ts — bun:test didn't resolve under tsc. Added a scoped /// <reference types="bun-types" /> in a new root bun-env.d.ts (added to include) rather than a types allow-list, so automatic @types inclusion is preserved.

Verification

• bun run test → 13 pass / 0 fail
• ./node_modules/.bin/tsc --noEmit → exit 0, no errors

Assumptions / notes

• DataTable was left untouched. The task flagged a possible stale-closure sort bug, but all three DataTable tests already pass — handleSort is recreated each render with the current sortDir and fireEvent.click flushes state between clicks via act(). No change was required; making one would have been speculative.
• No test files were modified and no dependencies were added, per constraints.
• Reviewed via the review agent (verdict: sound, no blockers). Non-blocking follow-ups noted for a future PR: the once-per-render Button dev-warn could be de-duped, and @testing-library/jest-dom matcher types are not currently wired into bun:test (unchanged from baseline — wiring them would require editing a test-setup file, which was out of scope here).