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/defs/asrenderprops/readme.mdx

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+---
+title: Defs.asRenderProps()
+---
+
+Returns the Defs as render props, suitable for front-end rendering.
+
+## Signature
+
+```js
+Object defs.asRenderProps()
+```
+
+The object returned by this method will have a `list` property that
+holds all the defs, as well as a `asSvg` property that holds the result
+of [Defs.render()](/reference/api/defs/render):
+
+```js
+{
+  list: {
+    button: `<g id="button" transform="scale(1)">
+  <circle cx="0" cy="0" r="3.4" class="mark"></circle>
+  <circle cx="-1" cy="-1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="1" cy="-1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="1" cy="1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="-1" cy="1" r="0.5" class="no-stroke fill-mark"></circle>
+</g>`,
+  buttonhole: `<g id="buttonhole" transform="scale(1)">
+  <path class="mark" d="M -1,-5 L 1,-5 L 1,5 L -1,5 z"></path>
+</g>`,
+  },
+  forSvg: `
+<g id="button" transform="scale(1)">
+  <circle cx="0" cy="0" r="3.4" class="mark"></circle>
+  <circle cx="-1" cy="-1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="1" cy="-1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="1" cy="1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="-1" cy="1" r="0.5" class="no-stroke fill-mark"></circle>
+</g>
+<g id="buttonhole" transform="scale(1)">
+  <path class="mark" d="M -1,-5 L 1,-5 L 1,5 L -1,5 z"></path>
+</g>
+`
+}
+```

sites/dev/docs/reference/api/defs/clone/readme.mdx

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+---
+title: Defs.clone()
+---
+
+Returns a Defs object that is a deep copy of this one.
+
+## Signature
+
+```js
+Defs defs.clone()
+```

sites/dev/docs/reference/api/defs/get/readme.mdx

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+---
+title: Defs.get()
+---
+
+Returns the value of a defs entry stored under _name_.
+
+## Signature
+
+```js
+String defs.get(string name)
+```
+

sites/dev/docs/reference/api/defs/readme.mdx

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+---
+title: Defs
+---
+
+The `Defs` object in FreeSewing's core library represents an SVG document's
+[`defs` element](https://developer.mozilla.org/en-US/docs/Web/SVG/Element/defs).
+It is not directly exposed, but it is available as the `defs` attribute
+of an [Svg object](/reference/api/svg/defs).
+
+While the properties and methods exposed by this object are typically only used internally,
+they are documented here to facilitate development of plugins.
+
+## Properties
+
+A Defs object comes with the following property:
+
+- `list` : Holds the internal object in which entries of the `defs` element are stored
+
+## Defs methods
+
+<ReadMore />
+

sites/dev/docs/reference/api/defs/remove/readme.mdx

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+---
+title: Defs.remove()
+---
+
+Removes the defs entry stored under _name_.
+
+
+## Signature
+
+```js
+Defs defs.remove(string name)
+```
+
+This object is chainable as it returns the `Defs` object.
+

sites/dev/docs/reference/api/defs/render/readme.mdx

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+---
+title: Defs.render()
+---
+
+Renders the added Defs as a string suitable for inclusion in an SVG document `defs` element.
+
+## Signature
+
+```js
+String defs.render()
+```
+
+This function is called by [svg.render()](/reference/api/svg/render) internally.
+Its output will look something like this:
+
+```()
+<g id="button" transform="scale(1)">
+  <circle cx="0" cy="0" r="3.4" class="mark"></circle>
+  <circle cx="-1" cy="-1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="1" cy="-1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="1" cy="1" r="0.5" class="no-stroke fill-mark"></circle>
+  <circle cx="-1" cy="1" r="0.5" class="no-stroke fill-mark"></circle>
+</g>
+<g id="buttonhole" transform="scale(1)">
+  <path class="mark" d="M -1,-5 L 1,-5 L 1,5 L -1,5 z"></path>
+</g>
+```

sites/dev/docs/reference/api/defs/set/readme.mdx

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+---
+title: Defs.set()
+---
+
+Sets the defs entry stored under _name_ to _value_.
+
+## Signature
+
+```js
+Defs defs.set(
+  String name,
+  String value
+)
+```
+
+This object is chainable as it returns the `Defs` object.
+

sites/dev/docs/reference/api/defs/setifunset/readme.mdx

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+---
+title: Defs.setIfUnset()
+---
+
+Sets the defs entry stored under _name_ to _value_, but only if it 
+is not currently set to any value (if it is undefined).
+
+## Signature
+
+```js
+Defs defs.setIfUnset(
+  String name,
+  String value
+)
+```
+
+This object is chainable as it returns the `Defs` object.