Provide a single instance location so that views don't need to share handles anymore.

[pragmatrix]

Close #127

[Copilot]

Pull request overview

This PR addresses issue #127 by removing cross-subsystem sharing of mutable scene handles and instead introducing a single, stable instance root location that views can parent to, so the desktop can present instances without referencing view-local handle definitions that may not yet be ingested by the renderer.

Changes:

• Introduces Ref<T> as a read-only handle type and updates scene objects/ergonomics to use Ref for location/transform references.
• Adds InstanceRoot (transform + location) to provide a shared instance node for presenters and views, and updates desktop presentation flow to use it.
• Simplifies ViewCreationInfo and view creation so the desktop no longer receives/uses a view-provided Location handle.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
scene/src/transform_resolver.rs	Switches resolver caching/lookup to use Ref<Location> keys.
scene/src/objects.rs	Migrates Visual/Location to store Ref references instead of mutable Handles.
scene/src/handle.rs	Adds Ref<T> and HandleValue, and tightens update/change collection ordering in InnerHandle.
scene/src/ergonomics.rs	Updates positioning helpers (At, VisualWithoutLocation::at) to accept Ref<Location>.
desktop/src/instance_presenter.rs	Uses InstanceRoot and a shared instance location/transform node for background + view alpha.
desktop/src/instance_manager.rs	Introduces and stores InstanceRoot, and passes a Ref<Location> parent into InstanceContext.
desktop/src/desktop.rs	Updates command handling for the new DestroyView signature (no collector payload).
desktop/src/desktop_system/presentation.rs	Threads InstanceRoot through instance presentation.
desktop/src/desktop_system/command_dispatch.rs	Creates/passes InstanceRoot during instance spawn and presentation.
applications/src/view.rs	Parents view-local location under a provided parent Ref<Location>; removes sending desktop-owned location in CreateView.
applications/src/view_builder.rs	Carries parent: Ref<Location> through the builder into View::new.
applications/src/instance_context.rs	Stores a view_parent: Ref<Location> and changes DestroyView command payload.
.github/copilot-instructions.md	Adds repo orientation, boundaries, and validation guidance for future edits.