Sync local state with remote after untracked local evolution

Local site-ai/ had diverged significantly from the last commit pushed
to Gitea (new remote-env-setup/remove targets, SITE_CONFIG_DIR/MAIN_REPO
split, credential cleanup in server-install.sh, migration docs) without
ever being committed. This catches the repo up to what's actually on disk.

Also untracks the legacy user/ subtree left over from before content was
split into its own standalone repo (natascha-rieter.nl-user) — user/ is
gitignored here and stays a separate git repo, unaffected by this commit.

.gitignore

@@ -1,11 +1,11 @@
 # Environment
 .env
 
-# Grav CMS
-user/accounts/
-user/data/
-user/cache/
-user/plugins/
+# Grav CMS content (standalone repo, see README)
+user/
+
+# Local scratch / migration testing
+migration-test/
 
 # Claude
 .claude/