fix: repair cross-package bugs so bun test and tsc pass

[stooit]

Summary

Makes bun test && tsc --noEmit fully pass from the repo root (was 9 fail / 4 pass + 5 type errors → now 13 pass / 0 fail, tsc exit 0). Fixes four cross-package defects plus the test-runner config that was masking all of the UI failures.

Root causes & fixes

#	File	Bug	Fix
1	apps/web/src/lib/api.ts	Imported useThrottle, but the utils hook was renamed to useDebounce (broke the import and tsc)	Import useDebounce; keep the public useSearchDebounce alias unchanged
2	packages/ui/src/components/Button/Button.tsx	aria-label destructured but never applied to <button>	Pass it through with a children-derived fallback for icon-only buttons + dev-time warning when an icon-only button has no label
3	packages/ui/src/components/DataTable/DataTable.tsx	Sort toggle read captured sortDir (stale closure)	Functional updater setSortDir((prev) => …)
4	packages/utils/src/format/date.ts	en-AU numeric format emitted a leading zero on the day (01/03/2024)	Assemble via formatToParts so the day has no leading zero (1/03/2024)
5	bunfig.toml (root)	Used the non-Bun environment = "happy-dom" key — silently ignored, so document was undefined and every UI test errored	preload = ["./packages/ui/test/setup.ts"] so bare bun test works
6	tsconfig.json	bun:test unresolved	Add "types": ["bun-types"] (already installed)

All six UI test failures shared a single root cause (no DOM from #5); once fixed, the functional-updater change (#3) is defensive hardening of the flagged stale-closure area.

Verification

bun test        → 13 pass, 0 fail (17 expect() calls, 5 files)
bunx tsc --noEmit → exit 0, zero type errors

Constraints honoured

• No test files modified, no dependencies added (bun-types was already a devDependency).
• Tests treated as source of truth for correct names/behaviour.
• packages/ui/bunfig.toml left unchanged so per-package runs keep working.

Follow-ups (out of scope, non-blocking)

• Icon-only Button a11y: fallback label satisfies the test but a generic "Button" conveys nothing to a screen reader; a required aria-label when iconOnly (discriminated union) would enforce it at compile time.
• DataTable keyboard sorting: onClick on a bare <th> with no tabIndex/onKeyDown (WCAG 2.2 SC 2.1.1) — pre-existing.

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