Adds docs/marketing/community-listening-week1.md per ELF-51.
10 HN threads (requestbin / ngrok / self-hosted / single-binary Go)
with one-line engagement plans and explicit no-go lines.
Reddit half is deferred to ELF-58 because the JSON listing endpoint
was blocked by the network policy at draft time.
Reviewer: Head of Marketing.
Co-Authored-By: Paperclip <noreply@paperclip.ing>
