docs(rfcs): add RFC-0007 Figma Make Pipeline Integration (Signed Off)

Drops stale RFC-0006 + RFC-0008 from the original triple-RFC PR — both
already shipped to main with newer content (lifecycle frontmatter +
docs gate compliance via AISDLC-69.2 / AISDLC-118). Keeps only the
RFC-0007 deliverable, rebased onto current main and updated with the
canonical lifecycle frontmatter convention so `scripts/check-rfc-docs.mjs`
accepts it (status: Final, lifecycle: Signed Off, requiresDocs: []).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: deefactorial