ignore .worktrees as a "special folder" (#35835)

following the approach from nixpkgs that ignore the .worktrees folder,
we could also do the same, this would allow worktrees to be worked on in
the same folder as the primary branch.

ref:
b6420c7bca

.gitignore

@@ -124,3 +124,6 @@ prime/
 /AGENT.md
 /CLAUDE.md
 /llms.txt
+
+# Ignore worktrees when working on multiple branches
+.worktrees/