Six modules created a directory inside site-packages at import time with an
unguarded mkdir: backend/plugins.py (plugins/) and backend/{context,marketplace,
personas,tasks,mempalace_bridge}.py (data/). Where site-packages is not
writable -- a container running as a non-root user, a system-wide install --
the first one raised PermissionError while backend was still loading and took
the whole package down.

Both now go through backend.paths.resolve_writable_dir(): bundled dir first,
then DULUS_CONFIG_DIR / ~/.dulus, then temp, never raising. Same wound as the
~/.dulus crashes fixed in 3.10.20/21, in the remaining entry points.