[Preview NG] Export preview system hooks from @khanacademy/perseus-editor

[jeremywiebe]

Summary:

This PR is part of a series building a typed, hook-based preview system for the Perseus editor. The new system replaces the untyped window.iframeDataStore + raw postMessage(string) communication with structured, validated message passing via usePreviewController and usePreviewPresenter hooks. The new system is being built alongside the old one — no existing behavior changes until the final PR in the series flips the switch.

Previous PRs in this series:

• [Preview NG] Type findWidgets functions and add JSDoc to HintRenderer props #3464
• [Preview NG] Remove unused bold support from hint preview #3467
• [Preview NG] Add typed preview message protocol with validators #3474
• [Preview NG] Add functions to sanitize objects for sending to Preview #3492
• [Preview NG] Introduce hooks to manage preview communication #3495

---

Exports usePreviewController and usePreviewPresenter from the @khanacademy/perseus-editor package so they can be consumed by the frontend repo and other consumers. This is a small wiring PR — it adds four lines to the package's main index.ts.

Purely additive — no existing behavior is changed.

Issue: LEMS-3741

Test plan:

pnpm tsc and pnpm knip both pass. No new tests needed — the hooks are already fully tested in #3495.

[github-actions]

🗄️ Schema Change: No Changes ✅

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (1e606e2) and published it to npm. You
can install it using the tag PR3499.

Example:

pnpm add @khanacademy/perseus@PR3499

If you are working in Khan Academy's frontend, you can run the below command.

./dev/tools/bump_perseus_version.ts -t PR3499

If you are working in Khan Academy's webapp, you can run the below command.

./dev/tools/bump_perseus_version.js -t PR3499

[github-actions]

Size Change: +1.03 kB (+0.21%)

Total Size: 504 kB

📦 View Changed

Filename	Size	Change
packages/perseus-editor/dist/es/index.js	104 kB	+1.03 kB (+1%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	20.6 kB
packages/keypad-context/dist/es/index.js	1 kB
packages/kmath/dist/es/index.js	6.31 kB
packages/math-input/dist/es/index.js	98.5 kB
packages/math-input/dist/es/strings.js	1.61 kB
packages/perseus-core/dist/es/index.item-splitting.js	12 kB
packages/perseus-core/dist/es/index.js	25.5 kB
packages/perseus-linter/dist/es/index.js	9.41 kB
packages/perseus-score/dist/es/index.js	9.78 kB
packages/perseus-utils/dist/es/index.js	403 B
packages/perseus/dist/es/index.js	198 kB
packages/perseus/dist/es/strings.js	8.5 kB
packages/pure-markdown/dist/es/index.js	1.39 kB
packages/simple-markdown/dist/es/index.js	6.71 kB

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[github-actions]

🛠️ Item Splitting: No Changes ✅

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