[codex] web-design (rename vibe-builder and add extra skills)

[edward-bayes]

Overvoew

• Rename the vibe-builder plugin to web-design across the plugin folder, manifest, README, agent metadata, top-level repo docs, and marketplace registration.
• Expand the plugin with two additional frontend-oriented skills: react-best-practices and web-design-guidelines.
• Update the plugin copy so the default prompt and descriptions reflect UI review and React/web design workflows in addition to deployment, payments, and database guidance.

Validation

• Confirmed the git rename landed cleanly and the marketplace path now points to ./plugins/web-design.
• Verified the copied react-best-practices bundle includes its supporting files such as rules/, AGENTS.md, README.md, and metadata.json.
• No repo-wide automated test suite was run because this repository does not appear to have a single build/test entrypoint.