Add CLAUDE.md with pre-push verification guidance

Document running :java:checkstyleMain (Java-only, easy to miss) and
module compile tasks before committing/pushing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: sacOO7

CLAUDE.md

@@ -0,0 +1,20 @@
+# CLAUDE.md
+
+Guidance for Claude Code when working in this repository.
+
+## Before committing / pushing
+
+Run the relevant checks locally first — CI enforces them and a failure means another round-trip.
+
+- **Java changes** (`lib/`, i.e. the `:java` module): run **both**
+  ```
+  ./gradlew :java:compileJava :java:checkstyleMain
+  ```
+  Checkstyle is Java-only and is easy to miss because compilation alone passes. Common gotcha: **no star imports** — `import com.google.gson.*;` fails `AvoidStarImport`; list each type explicitly.
+- **Kotlin changes** (`liveobjects/`): run
+  ```
+  ./gradlew :liveobjects:compileKotlin
+  ```
+  (No Kotlin linter is configured, so compilation is the gate.)
+
+When a change spans both, run all three tasks before pushing.