Add configure.sh wizard and offer to run it after install

- system_setup/configure.sh: interactive first-time setup wizard that
  edits config.d/configure.conf, tests the encrypted home mount, and
  obtains a Nextcloud WebDAV token
- configure.md: short usage documentation for configure.sh
- system_setup/install.sh: after cloning the repo, ask whether to run
  configure.sh immediately (as the sudo-invoking user via su)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

system_setup/install.sh

@@ -440,9 +440,26 @@ echo
 echo "  OEMDRV device : $OEMDRV_DEV"
 echo "  Mounted at    : $MOUNT_POINT"
 echo
-echo "Next steps:"
-echo "  1. cp $MOUNT_POINT/config/setup_system.conf.dist \\"
-echo "        $MOUNT_POINT/config/setup_system.conf"
-echo "  2. Edit setup_system.conf with your domain, IPA/Nextcloud FQDNs, and paths."
-echo "  3. Boot the Kickstart installer — it will detect the OEMDRV partition automatically."
+
+# ── Optionally run configure.sh ───────────────────────────────────────────────
+
+CONF_SCRIPT="$MOUNT_POINT/system_setup/configure.sh"
+
 echo
+read -r -p "Run configure.sh now to set up your environment? [y/N]: " RUN_CONF
+if [[ "${RUN_CONF,,}" == "y" ]]; then
+    if [[ -n "$SUDO_USER" ]]; then
+        info "Running configure.sh as user '$SUDO_USER'..."
+        su - "$SUDO_USER" -c "bash '$CONF_SCRIPT'"
+    else
+        echo
+        echo "configure.sh must be run as a non-root user. Please run:"
+        echo "  bash $CONF_SCRIPT"
+    fi
+else
+    echo
+    echo "Next steps:"
+    echo "  1. Run: bash $CONF_SCRIPT"
+    echo "  2. Boot the Kickstart installer — it will detect the OEMDRV partition automatically."
+    echo
+fi