Add native Kotlin integration

[amankoli09]

Closes #395

Summary

• Add a native Kotlin OpenUI Lang runtime with typed component definitions, prompt generation, parsing, streaming parse state, state declarations, and Query/Mutation extraction.
• Add a Jetpack Compose renderer with a registry for custom native components, default primitives, and action callbacks.
• Add a minimal Android Compose sample app plus Kotlin package README and parser tests.

Testing

• git diff --cached --check
• Not run: gradle :openui-lang:test because Gradle is not installed in this environment.