[codex] fix deploy redirects

[Frichetten]

Summary

• Add the existing redirect map to mkdocs.deploy.yml, which is the config used by the production deploy workflow
• Fix the Claude magic string old-path redirect generation for gh-pages

Root Cause

The production deploy config defines its own list-style plugins block. MkDocs inheritance replaces list values, so the redirects plugin from mkdocs.yml was not active during the deploy build.

Validation

• git diff --check
• docker run with mkdocs.deploy.yml confirmed the old article path generates a redirect index.html pointing to ../../deprecated/claude_magic_string_denial_of_service/
• docker run with mkdocs.yml completed a strict build