chore(e2e): Add E2E GitHub Actions workflow

[floydkim]

Summary

• Add a new GitHub Actions workflow for E2E testing: .github/workflows/e2e-manual.yml.
• Support manual execution via workflow_dispatch with inputs:
  • app (example app name, default: RN0840)
  • platform (ios, android, or both)
• Run iOS and Android E2E using npm run e2e -- --app <app> --platform <platform>.

iOS Setup

• Run on macos-latest.
• Add Ruby/Bundler dependency caching via ruby/setup-ruby with bundler-cache.
• Add CocoaPods cache for ~/.cocoapods and Examples/<app>/ios/Pods.
• Select and boot an available iPhone simulator for the E2E run.

Android Setup

• Run on ubuntu-latest.
• Use Zulu JDK 17 (actions/setup-java).
• Add Gradle cache via gradle/actions/setup-gradle.
• Enable KVM for emulator performance/stability.
• Use reactivecircus/android-emulator-runner with API 35 (x86_64) and extended boot timeout.

Test Plan

• Trigger manually with:
  • gh workflow run e2e-manual.yml --ref github-e2e-workflow -f app=RN0840 -f platform=ios
  • gh workflow run e2e-manual.yml --ref github-e2e-workflow -f app=RN0840 -f platform=android
  • gh workflow run e2e-manual.yml --ref github-e2e-workflow -f app=RN0840 -f platform=both