chore: Port FreeSewing.dev to docusaurus

The replaces the NextJS site powering FreeSewing.dev with a Docusaurus
setup. It's part of my efforts to simplify FreeSewing's setup so we can
focus on our core value proposition.

sites/dev/docs/reference/api/part/config/stack/readme.mdx

@@ -0,0 +1,51 @@
+---
+title: Assigning parts to stacks
+---
+
+The optional `stack` property assigns the part to a specific
+[Stack](/reference/api/stack).
+
+It holds either a string with the stack name or a function which
+returns the stack name:
+
+```js
+const part = {
+  name: 'example.front',
+  stack: 'example.combined',
+}
+```
+
+```js
+const part = {
+  name: 'example.back',
+  stack: ({options}) => options.stack ? 'example.combined' : 'example.back',
+}
+```
+
+## Notes
+
+If `stack` is present, the part is assigned to the stack with the
+specified name.
+If multiple parts are assigned to the same stack, they will overlap
+in drafting and printing layouts.
+This is because parts in the stack are drafted within the same stack
+space.
+
+Otherwise, if the `stack` property is not present, the default behavior
+is to use the part's name as its stack name.
+
+- In a draft with only one set, this will result in each part having its
+own stack.
+With a default layout, the part will not overlap other parts because it is
+the only part drafted within its stack and stacks do not overlap.
+
+- In a draft with multiple sets, this will result in parts of the same name
+using the same stack.
+This is how we achieve the layered look of parts in sample drafts.
+
+:::note RELATED
+
+Please see [Stacks](/guides/designs/stacks) in the Design Guide for
+more information about how stacks can be used.
+
+:::