Converts the orphaned gitlink (160000 with no .gitmodules) into a proper
submodule pointing at the content remote, and absorbs user/.git into
.git/modules/user so linked worktrees can populate user/. Bumps the pin
from 75da83d to the current pushed origin/main (924cfc1) as a clean
baseline. Enables per-worktree user/ checkouts for parallel dual-repo work.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
