feat(ios): support bundled JS in debug builds

[adamTrz]

Summary

Fixes iOS Debug packaged-bundle loading for brownfield apps running without Metro.

This PR addresses the case where a consumed brownfield XCFramework is built in Debug and the host app wants to load the packaged JavaScript bundle instead of relying on a dev server.

Root cause

There were two separate issues:

1. Runtime resolution

• in Debug, the iOS runtime always preferred Metro and ignored the embedded main.jsbundle

2. Packaging

• even after adding a runtime opt-in for bundled JS in Debug, the simulator slice of the packaged BrownfieldLib.xcframework did not contain main.jsbundle
• React Native skips bundling for Debug simulator builds by default, so the packaged simulator artifact was not self-sufficient

What changed

Runtime

• adds preferBundledBundleInDebug to ReactNativeBrownfield
• extracts bundle URL selection into a small testable resolver
• keeps current Debug behavior unchanged by default
• when preferBundledBundleInDebug = true, Debug builds load the embedded bundle
• fixes bundleURLOverride fallback behavior when the override returns nil

Packaging

• after Debug iOS packaging, copies main.jsbundle from the device framework build product into the simulator framework build product
• re-merges BrownfieldLib.xcframework so the simulator slice also contains main.jsbundle
• keeps DX simple:
  • no new CLI flags
  • no extra Xcode env vars
  • no special simulator packaging flow

Validation / coverage

• documents the new opt-in in iOS / Expo docs
• adds native Swift tests for iOS bundle URL resolution
• adds CLI tests for Debug simulator bundle copying
• adds a generic iOS native tests CI job for Swift-based iOS tests

Repro note

This issue only reproduces when the consumed XCFrameworks are themselves built in Debug.

A Debug host app linked against Release-built XCFrameworks is a false negative, because the framework runtime has already been compiled without the Debug Metro branch.

Validation

• swift test in packages/react-native-brownfield/ios
• yarn workspace @callstack/brownfield-cli test src/brownfield/utils/__tests__/copy-debug-bundle-to-simulator-slice.test.ts
• yarn exec brownfield package:ios --scheme BrownfieldLib --configuration Debug
• verified that:
  • Debug-iphonesimulator/BrownfieldLib.framework/main.jsbundle exists
  • BrownfieldLib.xcframework/ios-arm64_x86_64-simulator/BrownfieldLib.framework/main.jsbundle exists
• manual repro flow with Debug-built XCFrameworks and Metro stopped

User impact

Host apps can now explicitly opt into running a Debug-built brownfield framework from the packaged bundle:

ReactNativeBrownfield.shared.bundle = ReactNativeBundle
ReactNativeBrownfield.shared.preferBundledBundleInDebug = true
ReactNativeBrownfield.shared.startReactNative()

With the normal Debug packaging flow, the packaged simulator XCFramework now includes the bundle needed for that opt-in to work without Metro.