fix: Python 3.11 compatibility for f-string backslash

- Extract newline character to variable before using in f-string
- Fixes SyntaxError on Python 3.11 and earlier versions
- Synced fix to all 11 design_system.py locations
- Bump CLI version to 2.1.2

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "uipro-cli",
-  "version": "2.1.1",
+  "version": "2.1.2",
   "description": "CLI to install UI/UX Pro Max skill for AI coding assistants",
   "type": "module",
   "bin": {