feat(storage): support configurable install root

Add a LuCI install-root input, persist the selected path in UCI,
and route install, status, backup, uninstall, and runtime scripts
through the configured storage root for new installs.

Reference: custom install root flow

luasrc/openclaw/paths.lua

@@ -0,0 +1,35 @@
+local M = {}
+
+local DEFAULT_INSTALL_ROOT = "/opt"
+
+function M.normalize_install_root(path)
+	if type(path) ~= "string" or path == "" then
+		return DEFAULT_INSTALL_ROOT
+	end
+
+	if path:sub(1, 1) ~= "/" then
+		return DEFAULT_INSTALL_ROOT
+	end
+
+	path = path:gsub("/+$", "")
+	if path == "" then
+		path = "/"
+	end
+
+	return path
+end
+
+function M.derive_paths(path)
+	local install_root = M.normalize_install_root(path)
+	local oc_root = (install_root == "/") and "/openclaw" or (install_root .. "/openclaw")
+
+	return {
+		install_root = install_root,
+		oc_root = oc_root,
+		node_base = oc_root .. "/node",
+		oc_global = oc_root .. "/global",
+		oc_data = oc_root .. "/data",
+	}
+end
+
+return M