Before, setting `Graph.options.foldingEnabled = false` on one `Graph` instance affected other instances too — because the `options` object was shared between them.
For example, switching to the Constituent story (which disables `Graph.options.foldingEnabled`) then back to another story relying on the default (`true`) would break folding: the folding icon disappeared and cells couldn't be collapsed anymore.
This could be seen with the `Collapse` and the `Folding` stories.

The bug exists at least as of version 0.14.0, but probably from the first version of maxGraph.

🔍 Root cause: `options` was defined via mixins as an object, but the internal `applyMixin` function probably copies
object references, not values — effectively making `Graph.options` global.

✅ Fix: move the `options` property directly onto the `Graph` class.
It's the only object-typed prop in our mixins, and we're planning to turn `FoldingMixin` into a plugin anyway — so this fix is simple and future-proof.

ℹ️ No impact for users, just internal code structure changes.

In addition, migrate Constituent.stories.js to TypeScript to ease future maintenance.

tbouffard marked this pull request as ready for review

tbouffard changed the title fix(graph): make Graph.options truly per-instance fix: make Graph.options truly per-instance