configure.sh: allow root and non-root execution

- install.sh: pre-create ks.cfg with o+w after permission setup so
  non-root users can overwrite it (OEMDRV root itself stays o=rX)
- install.sh: restore su drop to $SUDO_USER when it is set and not
  root; fall back to direct root execution otherwise
- configure.sh: remove the hard root check so both cases work
- configure.md: update docs to reflect root/non-root support

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

system_setup/configure.sh

@@ -8,11 +8,6 @@ SCRIPTDIR="$(cd "$(dirname "$0")" && pwd)"
 CONF_DIST="${SCRIPTDIR}/config.dist/setup_system.conf.dist"
 CONF_FILE="${SCRIPTDIR}/../config.d/configure.conf"
 
-if [[ "$EUID" -eq 0 ]]; then
-    echo "ERROR: This script must not be run as root." >&2
-    exit 1
-fi
-
 # Prompt for a single value; returns the old value unchanged if the user presses Enter.
 prompt_value() {
     local name="$1" current="$2" new_val

system_setup/install.sh

@@ -31,6 +31,11 @@ finish_install() {
     chmod ug=rwX,o=rX "$MOUNT_POINT" -R
     chmod o+w "$MOUNT_POINT/config" "$MOUNT_POINT/config.d"
 
+    # Create an empty ks.cfg at the OEMDRV root so non-root can overwrite it
+    # with configure.sh (the OEMDRV root itself is not world-writable).
+    touch "$MOUNT_POINT/ks.cfg"
+    chmod o+w "$MOUNT_POINT/ks.cfg"
+
     info "Done."
     echo
     echo "  OEMDRV device : $dev"
@@ -42,13 +47,12 @@ finish_install() {
     echo
     read -r -p "Run configure.sh now to set up your environment? [y/N]: " RUN_CONF
     if [[ "${RUN_CONF,,}" == "y" ]]; then
-        if [[ -n "$SUDO_USER" ]]; then
+        if [[ -n "$SUDO_USER" && "$SUDO_USER" != "root" ]]; then
             info "Running configure.sh as user '$SUDO_USER'..."
             su - "$SUDO_USER" -c "DISPLAY='${DISPLAY}' WAYLAND_DISPLAY='${WAYLAND_DISPLAY}' bash '$CONF_SCRIPT'"
         else
-            echo
-            echo "configure.sh must be run as a non-root user. Please run:"
-            echo "  bash $CONF_SCRIPT"
+            info "Running configure.sh as root..."
+            bash "$CONF_SCRIPT"
         fi
     else
         echo