chore: clean up temp files and deduplicate .gitignore

Remove 12 untracked temp/debug/validation files, delete .plugkit-browser-profile
directory, deduplicate .gitignore entries, and add patterns for underscore-prefixed
temp files, .codeinsight, and .plugkit-browser-profile/.

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

Author: lanmower

.gitignore

@@ -82,3 +82,8 @@ server*.log
 test-*.js
 run-test.sh
 kill
+
+# Temp/debug files (underscore-prefixed)
+_*
+.codeinsight
+.plugkit-browser-profile/