fix: resolve failing tests and type errors across monorepo

[stooit]

Summary

Makes bun test (13/13 pass) and tsc --noEmit (0 errors) green from the repo root. No test files modified, no new dependencies.

• apps/web/src/lib/api.ts — import renamed hook useDebounce (was stale useThrottle).
• packages/ui Button — forward aria-label; icon-only buttons without a label fall back to string children or "Button" with a dev-only console.warn (WCAG 4.1.2).
• packages/ui DataTable — fix stale closure in sort toggle with functional setSortDir(prev => ...).
• packages/utils formatDate — en-AU day-first output with unpadded day (1/03/2024) via formatToParts, since ICU en-AU pads the day otherwise.
• bunfig.toml — replaced Vitest-only environment = "happy-dom" (ignored by Bun) with preload of the existing happy-dom setup file.
• tsconfig.json — "types": ["bun-types"] (already a devDependency) to resolve bun:test.

Assumptions

• Test expectations define the desired date shape (unpadded day, padded month, 4-digit year).
• The "Button" fallback label is a test-satisfying safety net; callers should still pass a meaningful aria-label for icon-only buttons.
• Follow-ups (not done, out of scope): redundant --preload in the package.json test script, merge duplicate imports in api.ts, README "Known issues" now stale.