Creates a prototype user interface for dyna3 in the `app-proto` folder. The interface is dynamically constructed using [Sycamore](https://sycamore.dev).
The prototype includes:
* An application state model (the `AppState` type)
* A constraint problem model (the `Assembly` type), used in the application state
* Two views
* A 3D rendering of the assembly (the `Display` component)
* A list of elements and constraints (the `Outline` component)
The following features confirm that the views can reflect and send input to the model:
* You can select elements by clicking and shift-clicking them in the outline. The selected elements are highlighted in the display.
* You can add elements using a button above the outline. The new elements appear in the display.
Co-authored-by: Aaron Fenyes <aaron.fenyes@fareycircles.ooo>
Reviewed-on: glen/dyna3#14
Co-authored-by: Vectornaut <vectornaut@nobody@nowhere.net>
Co-committed-by: Vectornaut <vectornaut@nobody@nowhere.net>
