chore: register user/ as a git submodule

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>

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "user"]
+	path = user
+	url = ssh://git@m038-nas.tail63ee39.ts.net:222/m038/intotheeast-com-content.git
+	branch = main