Fix encoding issues in Android build

- Replaced non-ASCII arrow character in `AndroidScreenshotTask.java` with ASCII "->" to fix compilation error.
- Updated `Ports/Android/build.xml` to explicitly use `encoding="UTF-8"` for `javac` tasks.
- Updated `.ci/container/Dockerfile` to generate and enforce `en_US.UTF-8` locale in the build container.

Author: google-labs-jules[bot]

scripts/build-android-app.sh

@@ -64,7 +64,8 @@ export PATH="$JAVA_HOME/bin:$MAVEN_HOME/bin:$PATH"
 ANDROID_SDK_ROOT="${ANDROID_SDK_ROOT:-${ANDROID_HOME:-}}"
 if [ -z "$ANDROID_SDK_ROOT" ]; then
   if [ -d "/usr/local/lib/android/sdk" ]; then ANDROID_SDK_ROOT="/usr/local/lib/android/sdk"
-  elif [ -d "$HOME/Android/Sdk" ]; then ANDROID_SDK_ROOT="$HOME/Android/Sdk"; fi
+  elif [ -d "$HOME/Android/Sdk" ]; then ANDROID_SDK_ROOT="$HOME/Android/Sdk"
+  elif [ -d "/opt/android/sdk" ]; then ANDROID_SDK_ROOT="/opt/android/sdk"; fi
 fi
 if [ -z "$ANDROID_SDK_ROOT" ] || [ ! -d "$ANDROID_SDK_ROOT" ]; then
   ba_log "Android SDK not found. Set ANDROID_SDK_ROOT or ANDROID_HOME to a valid installation." >&2