docs(onlywatch): update README badges and build preview

- update Next.js badge from canary to v16
- refine technical concerns section title from performance to deploy and build
- update build preview screenshot to reflect Next.js v16 features
- replace `'use cache'` reference with `cacheComponents`

Author: aqzhyi

@apps/onlywatch.tw/README.md

@@ -15,7 +15,7 @@
 ![Supabase](https://img.shields.io/badge/Supabase-3ECF8E?style=for-the-badge&logo=supabase&logoColor=white)
 ![Better-Auth](https://img.shields.io/badge/Better--Auth-%23000000.svg?style=for-the-badge&logo=auth0&logoColor=white)
 ![Vercel](https://img.shields.io/badge/vercel-%23000000.svg?style=for-the-badge&logo=vercel&logoColor=white)
-![NextJS-canary](https://img.shields.io/badge/Next@Canary-%23333333?style=for-the-badge&logo=next.js&logoColor=white)
+![NextJS-v16](https://img.shields.io/badge/Next@v16-%23333333?style=for-the-badge&logo=next.js&logoColor=white)
 ![NextJS-App-Router](https://img.shields.io/badge/Next@App--Router-%23333333?style=for-the-badge&logo=next.js&logoColor=white)
 ![NextJS-RSC](https://img.shields.io/badge/Next@RSC-%23333333?style=for-the-badge&logo=next.js&logoColor=white)
 ![NextJS-PPR](https://img.shields.io/badge/Next@PPR-%23333333?style=for-the-badge&logo=next.js&logoColor=white)
@@ -74,9 +74,9 @@
 
 ## 🔋 Technical Concerns
 
-### ⚡ performance
+### ⚡ Deploy and Build
 
-- ✨ Next.js (app router) with `PPR` and `'use cache'` enabled
+- ✨ Next.js@^16 (app router) with `PPR` and `cacheComponents` enabled
 
   ![Build Step Preview](/@apps/onlywatch.tw/public/next-build-preview.png)