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

[stooit]

Summary

Fixes all failing tests and type errors in the monorepo. bun test → 13 pass / 0 fail, tsc --noEmit → clean (exit 0).

Four cross-package bugs (plus a related a11y fix), all resolved under the hard constraints: no test files modified, no dependencies added, only what the tests require.

Area	Bug	Fix
apps/web/src/lib/api.ts	Imported useThrottle from @e2e/utils, but the hook was renamed to useDebounce — broke the api test and tsc	Import useDebounce so the test and app resolve the same export
tsconfig.json	tsc couldn't resolve bun:test in the (immutable) test files	Added "types": ["bun-types"]
packages/utils/src/format/date.ts	Test asserts formatDate(...) matches /^1/, but output was zero-padded 01/03/2024	Un-pad the day → 1/03/2024 (en-AU, day-first, 4-digit year)
packages/ui/.../Button.tsx	Icon-only button had no accessible name (WCAG 2.2 SC 4.1.2)	Render aria-label on icon-only buttons + dev-time warning when omitted

Assumptions & decisions

• formatDate — the test file is immutable and asserts an unpadded leading day (/^1/), so producing 1/03/2024 is the only way to satisfy it. The docstring now documents this day-first / unpadded-day trade-off honestly. (A cleaner fix would relax the test assertion to /^0?1\//, but tests may not be modified.)
• DOM test env — replaced a no-op environment = "happy-dom" key in bunfig.toml with bun's preload pointing at the existing packages/ui/test/setup.ts. This is a small deliberate cleanup beyond the strict minimum: it removes misleading dead config and lets bun test run per-package (previously document is not defined unless invoked via the root script). No dependency changes — the DOM lib was already installed and wired via the test script.
• Button — the icon-only fallback ("Button") plus a dev-only console.warn satisfies the test without a breaking API change. A stronger follow-up is making aria-label compile-time mandatory via a discriminated union when iconOnly is true.

Follow-ups (out of scope — blocked by immutable tests)

• DataTable.tsx has a latent stale-closure bug in its sort handler that the "stale closure test" does not actually catch (the test's act-wrapped clicks flush a re-render between them). Worth a ticket.
• The formatDate / formatDateTime pair now emit different year widths — pre-existing inconsistency, left alone.

Verification

• bun test — 13 pass / 0 fail (ui 6/6, utils 5/5, web 2/2)
• bunx tsc --noEmit — clean
• No test files touched; dependencies/devDependencies byte-identical