Revert "chore: add .opencode/plans to gitignore"

This reverts commit c37b33a.

Author: zdrapela

.gitignore

@@ -81,7 +81,6 @@ dynamic-plugins-root/*
 .claude/settings.local.json
 .opencode/**/*.local.md
 .opencode/package-lock.json
-.opencode/plans/*
 
 # CI/Pipeline local overrides
 .ci/pipelines/shared_dir/*