feat: integrate poyraz-ui and reactive-switcher for theme management

- Added poyraz-ui preset CSS import to globals.css for styling.
- Created theme-switcher.md documentation for reactive-switcher usage.
- Added usage-guide.md for comprehensive Poyraz UI instructions.
- Updated package.json to include reactive-switcher as a dependency.
- Modified pnpm-lock.yaml to reflect the addition of reactive-switcher.
- Established themes.ts to export Poyraz UI themes for use in the application.

package.json

@@ -11,7 +11,8 @@
   "dependencies": {
     "next": "16.1.6",
     "react": "19.2.3",
-    "react-dom": "19.2.3"
+    "react-dom": "19.2.3",
+    "reactive-switcher": "^1.0.3"
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",