Add Redux & RTK complete guide and links

Add a new comprehensive guide react-interview/redux-rtk-guide.md covering plain Redux, Redux Toolkit, RTK Query, middleware, patterns, TypeScript, testing and interview Q&A. Also update index.md and react-handbook-part2.md to add prominent links to the new guide.

Author: adityaSrivastava29

index.md

@@ -34,6 +34,7 @@ layout: default
 - [Part 2 — State Management, Router, API Handling, Patterns, System Design](react-interview/react-handbook-part2)
 - [Part 3 — Machine Coding, Testing, Security, Build & Deploy, Micro Frontends](react-interview/react-handbook-part3)
 - [Part 4 — NPM Packages, 200+ Interview Q&A, Mental Models, Checklist, FAANG Internals](react-interview/react-handbook-part4)
+- [⚡ Redux & RTK Complete Guide — Plain Redux → RTK → RTK Query](react-interview/redux-rtk-guide)
 
 ---
 

react-interview/react-handbook-part2.md

@@ -141,6 +141,8 @@ const UIContext = createContext({}); // changes frequently (sidebar, modal)
 
 ## 6.3 Redux & Redux Toolkit (RTK)
 
+> 📖 **Deep dive:** [Redux & RTK Complete Guide](/react-interview/redux-rtk-guide) — Plain Redux from scratch → RTK Slices → RTK Query → Testing → Interview Q&A
+
 ### Architecture
 
 ```