fix(joint-react): register paper features synchronously during render

[kumilingus]

Summary

Fixes a class of bugs where features registered by hooks called inside a <Paper> subtree, or through a wrapping component (e.g. <PaperScroller> wrapping <Paper>), were not visible to sibling consumers in the same render pass. Adds adjacent fixes that surfaced while validating the main change.

Changes

1. Synchronous render-phase feature registration (use-create-features.ts)

Previously useCreateFeature deferred registration to useLayoutEffect. When a feature-registering component (e.g. <Snaplines />) mounted inside <Paper>, sibling consumers reading usePaperFeatures(paperId) in the same render captured an empty snapshot in their onLoad / imperative-API closures and never picked up the feature.

Fix: when target === 'paper' AND a paperStore is reachable AND the feature isn't already cached, register synchronously during render via createAndRegisterFeature + registerFeature. Mirrors the existing render-phase featureContext.features.set(...) path used when no paperStore exists. The featureRef.current guard in the existing useLayoutEffect re-register branch keeps onAddFeature firing exactly once.

2. Fallback paperStore lookup (use-create-features.ts)

When the hook is called outside a Paper subtree (e.g. <PaperScroller> wraps <Paper>, so the scroller sits above PaperStoreContext), usePaperStore(OPTIONAL) returns null. The deferred-queue path may have already registered the feature inside some paperStore, but useCreateFeature can't see it via context.

Fix: scan graphStore.papers for a paperStore whose features bag contains our id, fall back to it. Update / load paths now have a paperStore to operate on regardless of where the hook is mounted.

3. Existing-feature adoption (use-create-features.ts)

When the fallback paperStore resolves and a feature was already created via the deferred-queue path, the create-effect would have called onAddFeature again, producing duplicates. Adoption path: resolveExistingFeature(...) — if a feature with id already exists, store it in featureRef.current and skip creation.

4. <Paper> width/height routed through setDimensions (use-create-portal-paper.tsx)

width and height were spread into assignOptions(paper.options, ...), which mutated paper.options.width/height directly and bypassed the DOM update. Worse, it tripped setDimensions's early-exit guard the next time it ran (e.g. <PaperScroller> calling paper.setDimensions(...) after the prop change).

Fix: strip width/height out of the assignOptions spread and add a dedicated useEffect that calls paper.setDimensions(width, height). Keeps DOM CSS and paper.options in lockstep.

5. minPathMargin option in LinkRoutingOrthogonal preset (presets/link-routing.ts)

Surfaces the new minPathMargin option from the rightAngle router (joint-core #3266) on the orthogonal preset typings.

6. New @joint/react/stories subpath export

Adds a stories utility entry point so @joint/react-plus story files can reuse makeRootDocumentation, makeStory, and getAPILink without reaching into src/. Not part of the runtime public API.

• package.json — ./stories exports map entry
• rollup.config.ts — src/stories.ts added to entries
• src/stories.ts (new) — re-exports
• src/internal.ts — exposes OPTIONAL constant for downstream consumers

Test plan

• yarn jest --testPathPatterns="features|use-create" (43/43 pass)
• yarn typecheck (no new errors)
• Manual: <Snaplines /> mounted as child of <Paper> is detected by sibling <Stencil /> (validated downstream in joint-plus)
• Manual: <PaperScroller> wrapping <Paper> — feature registration / update / unmount paths all hit the same paperStore
• Manual: changing width/height props on <Paper> resizes the DOM, and <PaperScroller> setDimensions calls afterwards still work