fix: resolve cross-package test failures and type errors

[stooit]

Summary

bun test && tsc --noEmit now passes: 13 tests pass, 0 fail, and tsc exits 0. No test files or dependencies were changed.

• apps/web/src/lib/api.ts: the import used the old name useThrottle. It now imports useDebounce, which is what @e2e/utils exports.
• Button.tsx: icon-only buttons now always get an aria-label. The fallback now uses || instead of ??, so an empty label also falls back. When no label is given it falls back to string children, then to "Button". A warning still prints in dev mode.
• DataTable.tsx: fixed a stale-closure bug in the sort toggle by using the functional form of setState.
• date.ts: formatDate now gives en-AU d/MM/yyyy output, for example 1/03/2024. formatDateTime now reuses formatDate for its date part.
• tsconfig.json: added "types": ["bun-types"] so tsc can find bun:test. bun-types was already installed.
• bunfig.toml: this Bun version ignores environment = "happy-dom", so a plain bun test failed with document is not defined. I replaced it with a preload of the existing packages/ui/test/setup.ts.

Assumptions

• The formatDateTime output changes (1/3/24 becomes 1/03/2024) even though no test covers it. I kept it so it matches the DD/MM/YYYY format the docs describe; it can be reverted if preferred.
• Dates are still formatted in the host's timezone. I didn't hard-code a timezone.
• The generic "Button" fallback label is only a safety net; callers should pass a real aria-label.