Landing page: one static page for the search phrases that matter

[tosinamuda]

User story
As a searcher typing "AI markdown editor for macOS" or "Claude Code writing app", I want a landing page that answers in five seconds, so that I don't need to decode a GitHub repo to decide.

Acceptance criteria

• One static page: wedge headline, demo video/GIF, three only-Compose points, download (brew + dmg), honest alpha note
• Reuses docs/positioning.md copy (single source of truth)
• Targets the search phrases above (title/meta/h1)

Sub-tasks

• Pick host (GitHub Pages is fine v1)
• Build page from positioning doc
• Link from README + repo website field