Deprecate Claude magic string article

[Frichetten]

Summary

• Move the Claude magic string denial-of-service article into the AI/LLM deprecated section
• Add a prominent deprecation warning noting Anthropic patched the behavior as of May 2026
• Add a redirect from the old exploitation article path to the new deprecated path

Validation

• git diff --cached --check
• docker run --rm -v /Users/nick/Documents/hackingthe.cloud:/docs mkdocs-material build --strict --site-dir /tmp/htc-pr-site