Add experimental SwiftUI preview runner

[AryanRogye]

Description

This PR adds an experimental proof-of-concept SwiftUI preview runner for CodeEdit.

The goal is to explore rendering SwiftUI #Preview content directly inside the editor. When a Swift file contains a #Preview, CodeEdit can show a preview canvas next to the source editor, generate a temporary preview package, build it, dynamically load the compiled output, and render the resulting SwiftUI view inside the app.

Changes include:

• Adds SwiftSyntax-based #Preview detection and extraction
• Adds a preview pipeline: source processing → temporary package generation → build → dynamic load → render
• Adds a SwiftUI preview canvas inside the editor
• Adds AppKit hosting support for rendering the compiled preview view
• Links SwiftSyntax and SwiftParser for source processing
• Temporarily disables App Sandbox so the preview runner can build and dynamically load generated preview code

This is intentionally a proof of concept, not the final preview architecture.

Important limitations:

• Currently works best for self-contained SwiftUI files.
• Previews that depend on broader project/module context may not compile yet.
• Dynamic preview execution requires sandboxing to be disabled.
• The final security model should likely run previews in a separate helper process instead of loading arbitrary preview code into the main CodeEdit process.

Related Issues

#140

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

[AryanRogye]

⚠️ This is not meant to be merged as-is. I opened this PR to get early maintainer feedback on whether this direction is worth continuing.