[codex] Add Android app wrapper and 2026 conference assets

[d-date]

Summary

• add a native Gradle Android app wrapper around the Skip-generated Android target
• package schedule, sponsor, and organizer JSON/assets into the Android app, including 2026 conference content
• update Android build/run docs and Makefile flow, plus a small iOS sponsor card presentation tweak

Why

The Android target needed a first-class app project and bundled resources so the latest conference content can be installed and run directly with Gradle instead of relying on generated wrapper state.

Impact

• Android builds/install flow now goes through Android/gradlew app:installDebug
• Schedule, sponsors, and organizer data/assets are available as packaged resources in the Android app
• iOS sponsor cards use a simplified visual treatment

Validation

• Not run in this publish pass