Marketing Cold Email

Read the shared Stacks workflow, then
PLAYBOOK.md before doing this task. Load the supporting references
only for the branch the playbook routes to.

This ports cold-email from
coreyhaines31/marketingskills.
NOTICE.md records the snapshot and LICENSE retains the
upstream MIT notice.

Stacks integration

Keep marketing recommendations distinct from application API facts. Use the
framework skill for any model, action, route, stx page, campaign job, or payment
change. Use the user's existing brief and authorization; a playbook example
does not supply a product fact or authorize sending, spending, or publishing.

Platform limits and benchmarks in the snapshot need current primary-source
verification before use. Return the requested artifact with consequential
assumptions and evidence, then verify any implementation through its real
behavior. Use TypeScript and Bun for executable helpers.