Add RCS registration studio intake

[rightonq-code]

Summary

• Adds the standalone RCS registration studio under /rcs-registration/.
• Wires Part A submissions to the RightOnQ Google Sheet via the deployed Apps Script web app.
• Includes Apps Script project metadata and deployment notes for the intake receiver.

Verification

• Inline script syntax check passed.
• git diff --check passed for the RCS app and Apps Script files.
• Live Apps Script health check returns ok: true.
• Direct POST and local-browser form submission both appended to the intake Sheet, then test rows were removed.

Notes

• The root homepage file was deliberately not staged or changed as part of this branch.
• GitHub Pages currently serves main at www.rightonq.co.uk, so /rcs-registration/ will not be public until this branch is merged or another Pages deployment route is chosen.