docs: remove product-specific coupling language

[chubes4]

Summary

• Replaces named product-consumer references in transfer readiness docs with generic parent-control-plane language.
• Keeps WP Codebox framed as a consumer-agnostic sandbox/runtime/artifact substrate.
• Removes the named product integration section in favor of generic parent integration without coupling guidance.

Testing

• Not run; docs-only change.
• Verified no studio-web, Studio Web, or studio_web references remain under docs/, packages/, or tests.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafting the docs cleanup and verification steps; Chris reviewed the direction and requested the PR.