docs: clean up broken links and add GraphQL query formatter

[talhaamin221]

Hello! I audited the links in your README and found several resources that have gone dead, return timeouts, or have invalid SSL certificates.

To keep the curation list healthy, I have cleaned them up and added a new, modern developer helper:

1. Dead Link Cleanup:

• FakeQL (Mocking service is defunct) ➔ Removed
• Gitstar (Social feed is defunct) ➔ Removed
• Kotlin DSL Client (Medium blog is dead) ➔ Unlinked
• GraphQL Shorthand Notation Cheatsheet (Medium blog SSL expired) ➔ Pointed to official GraphQL.org Schema Documentation
• GraphQL Security Academy (Platform down/returning 502) ➔ Pointed to official OWASP GraphQL Security Cheat Sheet

2. New Tool Addition:

• Added Smart Formatter - GraphQL Query Formatter under Tools - Editors & IDEs & Explorers. It is a client-side, browser-only tool to format, beautify, and validate queries and schemas instantly.

This helps maintain list freshness and ensures users don't land on dead pages. Thank you for maintaining this list!