Clean up codebase and prepare as template

Remove unused files and code:
- Delete test/debug endpoints (test.get.ts, public.get.ts, user.get.ts, debug-config backup)
- Remove unused OAuth wrapper (oauth-authentik.ts)
- Clean up debug console.log statements
- Simplify code comments

Fix TypeScript errors:
- Add @types/node dependency
- Create index.d.ts with User interface extension
- Fix UButton color props (red→error, gray→neutral)
- Add type assertions in protected.get.ts

Update documentation:
- Enhance README.md as template documentation
- Update SETUP.md with correct API routes (/api/auth/* instead of /auth/*)
- Add NUXT_OAUTH_AUTHENTIK_SERVER_URL_INTERNAL documentation
- Update endpoint documentation

This commit prepares the repository to be used as a template for future Nuxt 4 + Authentik OAuth projects.

nuxt4-app/package.json

@@ -17,5 +17,8 @@
     "typescript": "^5.9.3",
     "vue": "^3.5.22",
     "vue-router": "^4.5.1"
+  },
+  "devDependencies": {
+    "@types/node": "^24.7.2"
   }
 }