add comprehensive javadoc comments for all classes

- Add class-level documentation for all mapper and multilingual classes
- Add complete javadoc for all public methods with @param and @return tags
- Add field-level comments for better code readability
- Improve documentation for initialization blocks and constructors

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

.gitignore

@@ -1,3 +1,7 @@
+/.claude
+/CLAUDE.md
+/AGENTS.md
+
 target/
 !.mvn/wrapper/maven-wrapper.jar
 !**/src/main/**/target/