Standalone macOS application builder

[Orbiter]

This PR adds a self-contained macOS version of SketchForge under apps/mac.

The generated application wraps the existing Next.js editor in a native
AppKit/WKWebView shell and bundles everything required to run it locally,
including Node.js, the standalone web server, static assets, and the MCP
adapter.

Changes

• Add a native macOS launcher using AppKit and WKWebView
• Build an isolated, MCP-enabled Next.js standalone server
• Bundle the appropriate Node.js runtime for the current Mac architecture
• Start the internal server on 127.0.0.1:3000 and stop it when the app closes
• Include a relocatable STDIO launcher for the SketchForge MCP server
• Bundle the SketchForge MCP skill inside the application
• Add application metadata and icon generation
• Add scripts for building SketchForge.app and packaging it as a DMG
• Store projects and logs under the user's Application Support directory
• Document installation, MCP configuration, architecture, and release checks
• Document the Gatekeeper approval required for ad-hoc-signed builds

Build

npm ci
apps/mac/build-app.sh
apps/mac/build-app-dist.sh

The resulting artifacts are written to:

apps/mac/dist/SketchForge.app
apps/mac/dist/SketchForge.dmg

[Orbiter]

An example Mac App build can be found here: https://github.com/Orbiter/SketchForge-3D-App/releases