fix: resolve cross-package test failures and type errors

[stooit]

Summary

Fixes all failing tests and type errors across the monorepo. Before: 5 failing tests + a tsc type error. After: 13/13 tests pass (bun run test) and tsc --noEmit exits 0.

Bugs spanned all three packages (packages/ui, packages/utils, apps/web):

• Hook rename mismatch (utils + web): the debounce hook was renamed but consumers drifted. apps/web/src/lib/api.ts imported the non-existent useThrottle, while the test asserts useSearchDebounce is the exported name. Made useSearchDebounce canonical end-to-end — renamed the hook file/function, updated the barrel export in packages/utils/src/index.ts, and fixed the apps/web import/re-export. The public export name from api.ts is unchanged, so downstream consumers are unaffected.
• Button aria-label not applied (ui): the aria-label prop never reached the rendered <button>. Now forwarded to the element, and icon-only buttons derive a non-null accessible name (WCAG 2.2 SC 4.1.2). aria-hidden on the decorative icon is applied only when the button already has an accessible label, so it can never strip the accessible name.
• DataTable stale-closure (ui): consolidated split sortKey/sortDir state into a single object updated via a functional setState, so repeated clicks toggle sort direction robustly even under batched/StrictMode re-renders.
• Date format (utils): formatDate kept en-AU field order and separators but the day was zero-padded (01/03/2024). Now strips the leading zero on the day via formatToParts -> 1/03/2024, satisfying the test while preserving DD/MM/YYYY ordering. currency formatting untouched.
• tsconfig (bun:test resolution): added "types": ["bun-types"] so bun:test imports resolve and tsc --noEmit exits cleanly. This is a config file, not a test file.

Assumptions & decisions

• The test files are the source of truth and were not modified (per the task constraints). Where the tests dictate a specific shape (canonical hook name useSearchDebounce, day format matching /^1/, non-null aria-label on icon-only buttons), the source was changed to match.
• Scope kept minimal. A code review flagged two initially-introduced changes that went beyond what tests required — a hard-coded type="button" (which would silently break form submission) and an over-broad aria-hidden that could remove a button's accessible name. Both were reverted/tightened so no consumer behaviour changed beyond the fixes the tests demand.
• No new dependencies added; bun-types was already in devDependencies.

Verification

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

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