Shared controls for native adapters

The existing Engine package also owns the control implementation used by Capacitor Native UI.
No additional npm package or workspace is required.

• @webview-native-ui/engine: generic projection API; unchanged dependency boundary.
• @webview-native-ui/engine/controls: control runtime and transport contract.
• @webview-native-ui/engine/controls/ionic: optional Ionic overlay implementation.
• @webview-native-ui/engine/integration: the single shared transition/search integration state.

An adapter creates one createNativeUI({ plugin, getPlatform, isAvailable }) instance and keeps it
for its lifetime. The plugin implements the NativeUIPlugin transport interface. The adapter owns
host registration, method dispatch, listener delivery, and lifecycle hooks; Engine owns rendering,
DOM ownership, extension acknowledgement, and teardown sequencing. Cordova can supply this same
transport without importing Capacitor. The Cordova Native UI plugin itself is a subsequent change.

SwiftPM exposes the optional WebViewNativeUIControls product, depending on WebViewNativeUIEngine.
CocoaPods exposes WebViewNativeUIControls with the same dependency. Android exposes the optional
io.github.webview-native-ui:controls artifact from android/controls; it depends on engine and
Compose. Generic Engine consumers keep their existing dependencies and Android minimum SDK 23.
Controls require Android API 24. Native adapters create NativeUIController and forward requests
and events. iOS receives JSON dictionaries and completion closures; Android receives JSONObjects.

The Ionic theme imports Engine integration directly. The Capacitor compatibility integration export
re-exports that module. Resolve a single Engine version in the application; do not bundle a private
copy of integration into the theme or adapter. The /controls entry does not load Ionic runtime code;
load /controls/ionic only when opting into Ionic overlays.

Verification and release order

Run npm run test:controls for the migrated control tests and npm test for generic projection.
SwiftPM's WebViewNativeUIEngine-Package scheme covers both native targets. Android's
:controls:testReleaseUnitTest covers the migrated snapshot parser. Existing Capacitor transport
and hosted lifecycle tests remain in its repository, and the theme retains the real demo E2E suite.

Build and verify Engine first, including both signed Maven artifacts in the same Central bundle and
both npm-distributed podspecs. Release the Engine native artifacts and npm package at the same version
before refreshing the Capacitor and theme registry lockfiles. Candidate verification uses local npm
tarballs and a temporary SwiftPM path or local Maven repository; do not commit these temporary paths.