fix bmad setup: create staging dirs without mode so _bmad is readable on Windows

mkdir(mode=0o700) yields an owner-only ACL on Windows with Python 3.13+,
leaving _bmad unreadable after the rename. Use the default mode instead.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sk72AxLwQnYttF6VFSxQLt

.agents/skills/bmad/scripts/setup.py

@@ -2238,7 +2238,7 @@ def materialize_bmad(
     # for a name collision and tries the next name, some two billion times. Setup
     # would hang in a folder it cannot write to instead of reporting the failure.
     staging = project_root / f"_bmad.setup-{os.urandom(8).hex()}"
-    staging.mkdir(mode=0o700)
+    staging.mkdir()
     try:
         # Seed staging so custom/, extra *.user.toml, and leftovers
         # survive replace_dir.