The global user layer was lowest priority, meaning installer-generated
defaults in _bmad/config.user.toml always shadowed it. Reorder so
global user preferences override installer defaults but are still
overridden by hand-authored project customizations.
New order for resolve_config.py:
base_team → base_user → global_user → custom_team → custom_user
New order for resolve_customization.py:
defaults → global_user → team → user
Users working across multiple worktrees or repos no longer need to
re-enter personal settings (user_name, communication_language,
user_skill_level) in every project. A global user layer at
~/.bmad/config/config.user.toml is merged as the lowest-priority
fallback in both resolve_config.py (5-layer) and
resolve_customization.py (4-layer). Project-level overrides always
win. Missing global dir is fully backward-compatible.
Closes#2338