chore(uninstall): --skip-rootless alias + clearer naming on the keep-the-layer flag

The existing --skip-docker-images flag keeps a lot more than just images:
the docker-install user, the rootless dockerd, the rootless sysctl
drop-ins, AND the image/build cache. So a reinstall after using it
already skips the slow `dockerd-rootless-setuptool.sh install` step —
which is the meat of why anyone reaches for this flag on a local dev
loop. The name "--skip-docker-images" undersells what it actually does
and "skip the rootless install" is the user-facing intent.

Adds --skip-rootless as an alias of --skip-docker-images (same flag
variable, no behaviour change). Both spellings continue to work — anything
scripting the old name keeps working — but the help text, examples, and
the uninstall printf now use the clearer --skip-rootless. Same name
shift in scripts/update.sh: SKIP_ROOTLESS=1 is the new env-var spelling,
SKIP_DOCKER_IMAGES=1 is the back-compat alias.

Signed-off-by: librelad <librelad@digitalangels.vip>

init.sh

@@ -10,11 +10,15 @@
 #   --unattended        Run in unattended mode (skip confirmations)
 #   --skip-os-update    Skip operating system update
 #   --skip-prereqs      Skip installing prerequisite apps
-#   --skip-docker-images On UNINSTALL: keep the rootless docker daemon, the
+#   --skip-rootless      On UNINSTALL: keep the entire rootless layer (the
-#                        docker-install user, and the image/build cache instead
+#   (also: --skip-docker-images)
-#                        of tearing them down — so a following reinstall rebuilds
+#                        docker-install user, the rootless dockerd, the sysctl
-#                        the WebUI image from cache (fast) instead of from
+#                        drop-ins, and the image/build cache) instead of tearing
-#                        scratch. (No effect on install.)
+#                        them down. A following reinstall then skips the slow
+#                        `dockerd-rootless-setuptool.sh install` step entirely
+#                        and rebuilds containers from the existing image cache,
+#                        which on local dev iteration cuts reinstall time from
+#                        minutes to seconds. (No effect on install.)
 #   --system-dir=PATH    Install root for the control plane (configs/logs/install/
 #                        db). Default /libreportal-system. (Also: LP_SYSTEM_DIR.)
 #   --containers-dir=PATH  Root for live app data. Default /libreportal-containers.
@@ -31,7 +35,7 @@
 #   ./init.sh --random-password --local init
 #   ./init.sh --random-password --local --unattended init
 #   ./init.sh --random-password --local --skip-os-update --skip-prereqs init
-#   ./init.sh --unattended --skip-docker-images uninstall   # keep docker layer
+#   ./init.sh --unattended --skip-rootless uninstall        # keep rootless layer for fast reinstall
 #   ./init.sh init mypassword myuser mytoken https://github.com/user/repo.git
 #
 
@@ -254,10 +258,17 @@ for ((i=1; i<=$#; i++)); do
             init_skip_prereqs=true
             ((init_shift_count++))
             ;;
-        --skip-docker-images)
+        --skip-docker-images|--skip-rootless)
             # On uninstall: preserve the rootless docker layer (daemon +
-            # docker-install user + image/build cache) so the next reinstall's
+            # docker-install user + sysctl drop-ins + image/build cache)
-            # `docker build` is cache-fast. Honored in runFullUninstall.
+            # so the next reinstall's `docker build` is cache-fast AND
+            # the slow `dockerd-rootless-setuptool.sh install` step is
+            # skipped. Honored in runFullUninstall.
+            #
+            # Two spellings: --skip-docker-images is the original name;
+            # --skip-rootless is the clearer alias (the flag keeps a lot
+            # more than just images). Both set the same flag, so passing
+            # either or both has the same effect.
             init_skip_docker_images=true
             ((init_shift_count++))
             ;;
@@ -1641,11 +1652,12 @@ runFullUninstall()
 	iuser=$(grep -h '^CFG_DOCKER_INSTALL_USER=' "${configs_dir}general/general_docker_install" 2>/dev/null | head -1 | cut -d= -f2 | awk '{print $1}')
 	iuser="${iuser:-dockerinstall}"
 
-	# --skip-docker-images: keep the rootless docker layer (the daemon, the
+	# --skip-rootless (alias: --skip-docker-images): keep the entire rootless
-	# "$iuser" user, the image/build cache + the rootless sysctl drop-in) instead
+	# layer (the daemon, the "$iuser" user, the image/build cache, and the
-	# of tearing it down, so a following reinstall's `docker build` is cache-fast
+	# rootless sysctl drop-ins) instead of tearing it down, so a following
-	# instead of from-scratch. Everything else (control plane, manager, footprint,
+	# reinstall skips the slow `dockerd-rootless-setuptool.sh install` AND
-	# /docker) is still removed.
+	# rebuilds from the existing image cache. Everything else (control plane,
+	# manager, footprint, /docker) is still removed.
 	local keep_docker="${init_skip_docker_images:-false}"
 
 	isHeader "LibrePortal — FULL Uninstall"
@@ -1675,7 +1687,7 @@ runFullUninstall()
 	printf "  ${GREEN}Left in place:${NC} ${DIM}docker engine, docker-compose, apt-installed deps, and your SSH config (so you can't get locked out).${NC}\n"
 	echo ""
 	if [[ "$keep_docker" == "true" ]]; then
-		isNotice "--skip-docker-images: KEEPING the rootless docker daemon, the '$iuser' user, and the image/build cache (for a faster reinstall)."
+		isNotice "--skip-rootless: KEEPING the rootless docker daemon, the '$iuser' user, sysctl drop-ins, and the image/build cache (for a faster reinstall)."
 		echo ""
 	fi
 	if [[ "$init_unattended_mode" == true ]]; then