test(web): add a DOM test environment and cover the core invariants

[PunGrumpy]

Why

No hook, component, or provider in the web app had any test, because no DOM environment was installed and `renderHook` had nothing to render into. That left the app's core machinery unverified:

• `hooks/use-optimizer.ts` owns object-URL lifetimes, batch supersession via a generation map, and the 300 ms quality debounce. A regression there silently leaks blob URLs or commits a stale result.
• `lib/compress/pool.ts` documents two invariants (at most `limit` in flight, start order preserved) that nothing asserted.
• The three limit constants in `lib/image/constants.ts` claim by comment to mirror `packages/core/types.go`, with a comment as the only enforcement.

What changed

• `happy-dom` + `@happy-dom/global-registrator` + `@testing-library/react` as dev dependencies, registered through `bunfig.toml` preload. The 43 pre-existing tests pass unchanged under the DOM registration.
• `pool.test.ts`: concurrency ceiling, start order, fewer-items-than-limit, and a characterization that a rejecting task rejects the whole batch (the documented contract).
• `limits-parity.test.ts`: reads `packages/core/types.go`, parses the Go literals without `eval` (handles both `20 << 20` and `100_000_000` forms), and asserts equality with the TS constants. Drift in either language now fails `bun test`.
• `use-optimizer.test.tsx`: five characterization tests through `renderHook` with deferred compression mocks: batch completion, supersession (the stale result is discarded and its URL revoked), removal mid-flight, unmount revoking every job URL, and the quality debounce under fake timers.

Notes for review

• `mock.module` in Bun patches the module registry for the whole test process. The browser-module mock therefore re-exports the real `readPreview`/`targetDimensions` (captured before mocking) so `browser.test.ts` keeps testing the genuine implementations in the same run.
• All five hook tests passed against the unmodified hook, so no behavior bug surfaced. They exist as the safety net for the upcoming cancellation work on this hook.
• This branch and ci: fail on format drift, freeze installs, and fix turbo cache keys #35 both touch `bun.lock`; whichever merges second needs a trivial rebase.

Verification

`bun test` in `apps/web`: 55 pass, 0 fail, 92 assertions across 10 files. `bun run typecheck` and root `bun run check` exit 0.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
pigo	Ready	Preview	Aug 30, 2026 2:09am
pigo-api	Ready	Preview	Aug 30, 2026 2:09am

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[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 72e0fe8.}