chore: remove .DS_Store artifacts and fix .gitignore

Remove tracked .DS_Store files from freebsd/prototypes/ and runtime/.
Drop the line in .gitignore that was explicitly re-including
freebsd/prototypes/.DS_Store, so the existing global .DS_Store rule
covers everything.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -108,4 +108,3 @@ yarn-error.log*
 
 # Allow keeping empty dirs with .keep
 !.keep
-freebsd/prototypes/.DS_Store