docs: plan namespace transfer

[chubes4]

Summary

• Adds a namespace transfer plan for Automattic ownership without renaming shipped WP Codebox code before target names are known.
• Inventories current @chubes4, chubes4/wp-codebox, plugin header, docs, examples, generated metadata, and smoke fixture assumptions.
• Keeps WP Codebox generic and separates product-specific consumers from the WP Codebox package/repository contract.

Verification

• npm run build
• npm run package-distribution-smoke
• npm run release:package

Closes #357.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the transfer plan documentation, inventoried namespace assumptions, and ran verification; Chris remains responsible for review and merge.