feat: add static product landing page for GitHub Pages

[Luis85]

Summary

• Adds site/index.html — a fully self-contained marketing landing page for the Flowti project
• Single HTML file with embedded CSS, zero external dependencies
• Designed to be served via GitHub Pages (configure Pages to serve from the site/ folder on this branch)

What's on the page

• Hero — primary tagline, live terminal output mockup, key stats (0 runtime deps, 5,920+ tests, 80%+ coverage)
• Problem / Solution — before/after comparison framing the pain Flowti solves
• Features — nine capability cards (build & test, health dashboard, reports, event catalog, scaffolding, project management, agent-native design, zero deps, sitemap UI)
• Living Testbed — dedicated section emphasising Flowti as a laboratory for new product ideas, with live/in-progress/planned experiment cards
• Ecosystem — three-layer breakdown of CLI, Plugin, and Agentonomous
• CTA + Footer — GitHub links

Test plan

• Enable GitHub Pages on this repo, source folder site/ on master
• Visit the published URL and verify the page renders correctly
• Check responsive layout at mobile widths (600px and below)
• Verify all GitHub links resolve correctly

https://claude.ai/code/session_01Hwbzoo9nR2xYeLvHn2Z65Z

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