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>

landing/assets/dash.svg

@@ -0,0 +1,9 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <rect width="512" height="512" rx="104" fill="#0a0a0a"/>
+  <g fill="#3b82f6">
+    <rect x="120" y="120" width="124" height="124" rx="28"/>
+    <rect x="268" y="120" width="124" height="124" rx="28" fill="#6b9ef8"/>
+    <rect x="120" y="268" width="124" height="124" rx="28" fill="#1d4fd7"/>
+    <rect x="268" y="268" width="124" height="124" rx="28"/>
+  </g>
+</svg>