chore: replace deprecated Resources.getColor and Gradle space-assignment DSL

[devin-ai-integration]

Summary

No SDK bump needed — launchdarkly-android-client-sdk is already pinned to 5.13.2, the latest 5.x on Maven Central. This PR only clears deprecation warnings that the build currently emits.

Two deprecations fixed:

• Resources.getColor(int) (deprecated since API 23) → ContextCompat.getColor(this, id) in MainActivity (5 call sites, both the initial render and the flag-change listener).
• Groovy DSL space assignment in app/build.gradle, which Gradle 9 warns "will fail with an error in Gradle 10":

  - namespace "com.launchdarkly.hello_android"
  - compileSdk 37
  + namespace = "com.launchdarkly.hello_android"
  + compileSdk = 37

  (also applicationId, versionCode, versionName, minifyEnabled, source/targetCompatibility)

One remaining Gradle 9 deprecation ("Using a Project object as a dependency notation") originates inside the Android Gradle Plugin, not this repo's scripts, so it is not actionable here.

How verified

• ./gradlew clean assembleDebug — BUILD SUCCESSFUL, and both the Kotlin getColor warnings and the namespace space-assignment warning are gone (verified with --warning-mode all).
• Installed the debug APK on an Android 36 x86_64 emulator with the hello-apps mobile key injected locally (never committed) and launched it; the app initialized the SDK and rendered the flag evaluation, confirming the ContextCompat.getColor styling path works at runtime:

Link to Devin session: https://app.devin.ai/sessions/7a61003c1e984050ad12233068fab8a3

[devin-ai-integration]

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