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

[stooit]

Summary

Fixes all failing tests and type errors across the monorepo. bun test && tsc --noEmit now reports 13 pass / 0 fail and tsc exit 0.

Bugs spanned all three packages plus test/type configuration.

Changes

• packages/utils + apps/web — a debounce hook was referenced under a stale name (useThrottle) that no longer existed. Reconciled the export in utils and updated apps/web/src/lib/api.ts to import the canonical useDebounce / expose useSearchDebounce as the tests expect.
• packages/ui/Button — icon-only buttons lacked an accessible name. Added aria-label wiring with a fallback of "Unlabelled button" (chosen over "Button" so the missing-label case stays visible to manual a11y audit / log review rather than being silently masked).
• packages/ui/DataTable — fixed a stale-closure bug in the sort handler (caught by the "sorts descending on second click" test) by moving sort key + direction into a single atomic SortState, avoiding nested/stale state updates under StrictMode.
• packages/ui/bunfig.toml + root bunfig.toml — the UI package's bunfig overrode the root config and dropped environment = "happy-dom", so UI tests ran without a DOM (document is not defined). Restored happy-dom for the UI tests while keeping the existing preload.
• packages/utils/date.ts — formatDate zero-padded day 1 (01/03/2024); switched to dateStyle: "short" so 1 March 2024 renders starting with 1, matching the test and consistent with formatDateTime.
• tsconfig.json — added bun types so bun:test resolves under tsc --noEmit (no test files modified).

Constraints honoured

• No test files modified.
• No new dependencies added (happy-dom and bun types were already installed).
• Scope limited to what the tests/types required.

Notes / assumptions for reviewers

• Date format: under bun's ICU, the numeric-parts alternatives still zero-pad the day for en-AU; dateStyle: "short" was the option that satisfied /^1/ while keeping the other date assertions green. Side effect: the year is now 2-digit. The test does not assert the year; flagged in case 4-digit years matter for your context.
• Button fallback is a visibility mechanism, not a hard gate — automated scanners still see a present accessible name. A stronger fix (required aria-label via a discriminated union when iconOnly) was out of scope as it would break tsc on the unmodifiable test file.

Verification

bun test         -> 13 pass, 0 fail
npx tsc --noEmit -> exit 0