feat(landing): static marketing page for Vercel

Single self-contained index.html under landing/ — no build step.
Product design tokens (dark theme, Geist + Geist Mono self-hosted,
#3b82f6 accent), hero with framed board screenshot, feature bento,
screenshots strip, install commands with copy buttons.

Deployed as Vercel project "dash" -> https://dash.vercel.app

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.gitignore

@@ -27,3 +27,4 @@ dist/
 # local tooling artifacts
 .playwright-mcp/
 .playwright-cli/
+.vercel