docs: add screenshots and redesign README with feature showcase

- Add 7 product screenshots (Dashboard, OrgChart, Messages, Tasks, Approvals, Documents, Onboarding)
- Redesign README with centered logo, badge row, nav links, and feature sections with screenshots
- Add supported AI runtimes table, tech stack table, and architecture overview
- Add landing/ to .gitignore (deployed separately to Cloudflare Pages)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -48,6 +48,9 @@ oldreference/
 # Local design scratch files
 homepagedesign.html
 
+# Landing page (deployed separately to Cloudflare Pages)
+landing/
+
 # Package manager logs
 npm-debug.log*
 pnpm-debug.log*