Remove stale .claude/worktrees gitlink; ignore the directory

The committed gitlink had no .gitmodules entry, so every CI checkout's
post-job cleanup failed with git exit 128 warnings.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: tig

.claude/worktrees/specs-beta-refresh

@@ -58,3 +58,6 @@ Thumbs.db
 .env.*
 !.env.example
 BenchmarkDotNet.Artifacts/
+
+# Claude Code session worktrees
+.claude/worktrees/