feat: add static landing page

Self-contained index.html under landing/ — no build step, deploys as a
plain static site (Vercel output dir = landing/). Uses the app's design
tokens (zinc dark, vermilion accent, Geist/Geist Mono vendored as woff2),
real screenshots from docs/, and the README feature/architecture facts.

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/primora.svg

@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64">
+  <rect width="64" height="64" rx="14" fill="#f4693a"/>
+  <g fill="#ffffff">
+    <rect x="15" y="14" width="34" height="10" rx="5"/>
+    <rect x="15" y="27" width="23" height="10" rx="5" opacity="0.7"/>
+    <rect x="15" y="40" width="10" height="10" rx="5"/>
+  </g>
+</svg>