[Apple 1/5] Create the native multiplatform SwiftUI foundation

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Goal

Create the native Apple-platform foundation for Anatomy Atelier, sharing application state and product logic across iOS/iPadOS, macOS, tvOS, and visionOS.

Scope

• Add an Xcode multiplatform app under apple/.
• Use SwiftUI with a shared app entry point and platform-specific scene composition where necessary.
• Establish shared feature, model, localization, asset, and test modules.
• Define minimum deployment targets based on the RealityKit APIs the product requires.
• Keep the existing web application intact.

Acceptance criteria

• The native app builds for iOS Simulator, macOS, tvOS Simulator, and visionOS Simulator.
• Each platform launches into a native Anatomy Atelier shell.
• Shared data and UI code are isolated from platform-specific presentation.
• Build and test commands are documented.
• No WebView is used for the native experience.

Sequence

This is step 1 of 5 and unblocks the shared RealityKit viewer.

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Implemented the native foundation on local branch codex/apple-platforms.

Completed in this vertical slice:

• XcodeGen-backed SwiftUI multiplatform app under apple/
• Shared app model, organ catalog, adaptive native library UI, and tests
• Platform-specific visionOS scene composition with no WebView
• Documented generation/build/test commands
• Successful Debug builds for macOS, iOS Simulator, tvOS Simulator, and visionOS Simulator
• 3 shared unit tests passing on macOS with serial test settings

Keeping this issue open until launch behavior has been reviewed on each simulator/device target.