Fix CI: remove hardcoded Java path from gradle.properties

Move machine-specific Java home to local.properties (gitignored)
so GitHub Actions can use its own JAVA_HOME.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: elliptic1

gradle.properties

@@ -11,8 +11,8 @@
 # The setting is particularly useful for tweaking memory settings.
 org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
 
-# Use Java 17 (has jlink for Android builds)
-org.gradle.java.home=/usr/lib/jvm/java-17-openjdk-amd64
+# Note: If you need to specify Java home locally, add to local.properties:
+# org.gradle.java.home=/path/to/jdk17
 
 # When configured, Gradle will run in incubating parallel mode.
 # This option should only be used with decoupled projects. More details, visit