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.

docker-compose.grav2.yml

@@ -0,0 +1,12 @@
+services:
+  grav2:
+    image: lscr.io/linuxserver/grav:2.0.21-ls271
+    container_name: natascha_grav2_test
+    environment:
+      - PUID=1000
+      - PGID=1000
+    ports:
+      - "8081:80"
+    volumes:
+      - ./migration-test/user:/config/www/user
+    restart: "no"