Fix edge function deploy failure caused by unescaped backticks in onboarding prompt

The memsprout onboarding tool (vello-mcp-v2) was broken since PR #401 — the Deno bundler failed to parse onboarding.ts because triple-backtick code fences inside the template-literal prompt string were closing the string early. The two fences are now escaped so the file parses correctly and the edge function deploys successfully again.