feat: native .icon format support for macOS Liquid Glass icons

[tsconfigdotjson]

Summary

• When mac.icons points to a .icon file (from Icon Composer), the build pipeline compiles it via xcrun actool, producing Assets.car (Liquid Glass on macOS 26+) and a .icns fallback for older macOS versions
• When mac.icons points to an .iconset folder, the existing iconutil path is unchanged — no breaking changes
• Adds CFBundleIconName to Info.plist when using .icon format (required for Assets.car lookup)
• Adds exit code checking for both actool and iconutil (previously failures were silently swallowed)
• Pre-checks for actool availability with a clear error message about requiring Xcode

Usage

// electrobun.config.ts
{
  build: {
    mac: {
      icons: "icon.icon", // from Icon Composer
    }
  }
}

Validation

Validated in a clean room build (/tmp/electrobun-cleanroom/):

• Cloned fresh from the branch, copied an .icon file into kitchen, set icons: "icon.icon" in config
• Ran bun dev:canary (codesign/notarize disabled)
• Confirmed Assets.car and AppIcon.icns both land in Contents/Resources/
• Confirmed Info.plist contains both CFBundleIconFile (AppIcon) and CFBundleIconName (icon)

actool compilation output:

Compiling .icon file with actool (requires Xcode)...
  output-files:
    .actool-partial-info.plist
    Electrobun Kitchen Sink-canary.app/Contents/Resources/Assets.car
    Electrobun Kitchen Sink-canary.app/Contents/Resources/icon.icns

Closes #121

🤖 Generated with Claude Code

[tsconfigdotjson]

@YoavCodes liquid glass icons