Add GitHub Pages landing site

[itsjithinv]

A single-file static landing/docs site for electron-ota, deployed to GitHub Pages at https://itsjithinv.github.io/electron-ota/.

What's included

• Hero with real npm install / CLI commands and version badges
• The model — renderer-OTA vs full-binary decision, as a mermaid flowchart
• Feature grid — signing, health-checked promotion, automatic rollback, deterministic rollouts, opaque bundles, atomic activation, anti-downgrade sequences, dashboard
• How it works — a mermaid sequence diagram (publish → verify → probation → heal) and a state diagram (the update lifecycle)
• Security model — the compromise-consequences table from the docs, plus renderer-confinement cards
• Architecture — a mermaid graph of the four npm packages + the two self-hostable apps
• CLI reference and hosting tiers (static tree vs cloud-api) tables
• Quickstart (the one-file integration) and a docs grid linking every guide

Notes

• Three mermaid diagrams render client-side (jsDelivr CDN), dark-themed to match the page. Verified rendering locally over HTTP — caught and fixed a sequence-diagram syntax error (angle brackets in a message).
• No build step; .nojekyll serves the file as-is.
• Deploy workflow (.github/workflows/pages.yml) triggers on pushes touching website/. Pages is already configured with GitHub Actions as the build source.
• Content reflects the current published packages (@electron-ota/{core,electron,cli,server-contract} @ 0.1.0) and newer features (S3 blob backend, sync, anti-downgrade sequences).