refactor(superdoc): type createSuperdocVueApp return shape (SD-2867 phase B) (#3057)

`createSuperdocVueApp()` returned `Object` per its JSDoc, so the five
fields SuperDoc.js destructures from the call (`app`, `pinia`,
`superdocStore`, `commentsStore`, `highContrastModeStore`) all
resolved to `Object` for any consumer enabling `// @ts-check`. Five
TS2339 'Property does not exist on type Object' errors at SuperDoc.js
line 464 — and inside the SD-2867 ratchet that turns each into a
gate failure.

Promotes the return type to a named `SuperdocVueAppRefs` typedef that
imports `vue.App`, `pinia.Pinia`, and the store types via
`ReturnType<typeof useSuperdocStore>` etc. The shape is internal-only
(this typedef is not on the public Modules / Config surface), so
adding it here doesn't widen the customer-visible surface.

Verified: pnpm --filter superdoc run check:jsdoc passes (3 gated files
clean); the consumer-typecheck matrix passes 31/31; the postbuild
declaration audit reports no FAIL findings; pnpm --filter superdoc
test passes 944/944.

This is groundwork for SD-2867 phase B: closing each cluster of
SuperDoc.js TS errors so the file can eventually enroll in
`CHECKED_FILES`. Five errors closed; ~133 remain across implicit-any
params, strict-null guards, and other type-not-assignable callsites.
Each cluster will land as its own focused commit.

Author: caio-pizzol

packages/superdoc/src/core/create-app.js

@@ -301,12 +301,24 @@ const setPiniaDevtoolsSuppressedForApp = (app, isSuppressed) => {
   };
 };
 
+/**
+ * Result of `createSuperdocVueApp()`. Internal-only: the shape is consumed
+ * by `SuperDoc.#initVueApp` and is not part of the public surface.
+ *
+ * @typedef {Object} SuperdocVueAppRefs
+ * @property {import('vue').App} app The Vue 3 app instance
+ * @property {import('pinia').Pinia} pinia The Pinia store instance attached to `app`
+ * @property {ReturnType<typeof useSuperdocStore>} superdocStore The SuperDoc Pinia store
+ * @property {ReturnType<typeof useCommentsStore>} commentsStore The Comments Pinia store
+ * @property {ReturnType<typeof useHighContrastMode>} highContrastModeStore The high-contrast mode composable refs (`isHighContrastMode`, `setHighContrastMode`). Named `*Store` for historical reasons; this is a plain Vue composable, not a Pinia store.
+ */
+
 /**
  * Generate the superdoc vue app
  *
  * @param {Object} [options]
  * @param {boolean} [options.disablePiniaDevtools=false] Disable Pinia devtools registration for this app instance
- * @returns {Object} An object containing the vue app, the pinia reference, and the superdoc store
+ * @returns {SuperdocVueAppRefs} An object containing the vue app, the pinia reference, the superdoc/comments Pinia stores, and the high-contrast mode composable
  */
 export const createSuperdocVueApp = ({ disablePiniaDevtools = false } = {}) => {
   const app = createApp(App);