chore: remove ANTLR .antlr/ cache files from tracking

These Java files are auto-generated by the ANTLR VS Code extension
for grammar preview/debug and are not used by the Go build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

.gitignore

@@ -20,6 +20,7 @@ go.work.sum
 .vscode/
 *.swp
 *.swo
+.antlr/
 
 # OS
 .DS_Store