Reddit review round: manual, README, licenses, release tooling, OG tags

- Single-source manual at docs/manual.md, rendered in the web app via
  marked (?raw import); README links to it instead of duplicating
- README rewritten around the hardware-review ask; keyboard tables removed
- Always-visible MANUAL/? buttons + first-visit auto-open (storage-safe)
- MIT license for code, CERN-OHL-S v2 for hardware/
- make release-artifacts TAG=<tag>: packages KiCad projects, review PDFs,
  gerbers and STEP into a zip and publishes a GitHub Release
- Open Graph/Twitter meta tags + screenshot for link previews
- Reddit post draft in docs/reddit-post.md
- Schematic review pack scripts (hardware/boards/scripts/review/)

Claude-Session: https://claude.ai/code/session_01T2bsDnnUwwpFXdCwKd65nL