feat(apple): add WebView bridge lifecycle

[birdmanmandbir]

Summary

• expose the Apple WebView string bridge and external URL opening
• detach the script handler, observer, and both JS references through one idempotent preparation path
• observe the app-kit pre-teardown notification without adding an app-kit package dependency
• preserve iOS behavior and guard all late native-to-JS delivery
• add a test-only addon proving exactly-once deletion of real JS references

Required app-kit notification/runtime contract: tta-lab/bare-app-kit commit f206059.

Verification

• npm test
• npm run test:native-lifecycle
• clean Darwin arm64 build
• clean iOS arm64 simulator build
• production addon contains no testing hooks