[codex] Add Hilt UI smoke test tooling

[caydyan]

Summary

• Configure the app instrumentation runner to use a Hilt test application.
• Add Hilt androidTest dependencies and kapt support.
• Add a minimal Espresso smoke test that launches MainActivity and verifies the primary UI host is visible.

Bounty

Addresses #736.

Bounty address: bc1qev5ant33v5y89qqjvcf4mh9hlax5svqf5xd7gc

Validation

• ANDROID_HOME=/opt/homebrew/share/android-commandlinetools JAVA_HOME=/opt/homebrew/opt/openjdk@17 ./gradlew :sphinx:application:sphinx:assembleDebugAndroidTest

[caydyan]

Current-head validation on 60c562d:

• git diff --check
• ANDROID_HOME=/opt/homebrew/share/android-commandlinetools JAVA_HOME=/opt/homebrew/opt/openjdk@17 ./gradlew :sphinx:application:sphinx:assembleDebugAndroidTest

The Android test APK builds successfully with the new Hilt runner and Espresso launch smoke test.