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.

.env.example

@@ -1,9 +1,36 @@
-REMOTE_USER=root
-REMOTE_HOST=example.com
-REMOTE_HOME=/home/example.com
-REPO=https://gitea.example.com/user/natascha-rieter.nl-user.git
-GRAV_VERSION=1.7.49.5
+# Copy to .env and fill in real values. .env is gitignored — never commit it.
+#
+#   cp .env.example .env
 
-GITEA_HOST=gitea.example.com
-GITEA_USER=natascha-deploy
-GITEA_TOKEN=your-token-here
+# ── SSH access to the production server ─────────────────────────────────────
+REMOTE_USER=
+REMOTE_HOST=
+REMOTE_PORT=22
+# Home directory of REMOTE_USER on the server. Used to derive WEBROOT and
+# SITE_CONFIG_DIR below unless you override those directly.
+REMOTE_HOME=
+
+# Override only if the site doesn't live at $REMOTE_HOME/public_html
+# WEBROOT=
+# Override only if the config repo shouldn't clone to $REMOTE_HOME/site-config
+# SITE_CONFIG_DIR=
+
+# Hostname production identifies itself as to Grav (used by
+# `make remote-configure-env` to pin git-sync's direction for this env —
+# see user/env/<host>/config/... in CLAUDE.md). Defaults to
+# nieuw.natascha-rieter.nl; override only if that changes.
+# REMOTE_ENV_HOST=
+
+# ── Gitea (content + config repos) ──────────────────────────────────────────
+GITEA_HOST=
+GITEA_USER=
+GITEA_TOKEN=
+
+# Git URLs for the two repos (used by `make remote-install` to clone them
+# onto a fresh server)
+USER_REPO=
+MAIN_REPO=
+
+# ── Grav ─────────────────────────────────────────────────────────────────────
+# e.g. 1.7.49.5
+GRAV_VERSION=