Remove accidental Claude worktree gitlinks from index

.claude/worktrees/ paths were committed as gitlink submodule entries,
breaking CI checkout with submodules:recursive. Removed from index
and added to .gitignore.

Author: w4nderlust

.claude/worktrees/agent-a7638c26

@@ -153,3 +153,6 @@ ludwig/benchmarking/configs/
 *.wav
 generated_audio/
 generated_images/
+
+# Claude Code worktrees (should never be committed)
+.claude/worktrees/