docs: redesign public README

[Vinaystwt]

Summary

• Reworked the public README into the approved product-page-plus-developer-reference structure.
• Added deterministic branded README assets under docs/assets/readme/ using the existing production logo mark.
• Replaced raw screenshots and Mermaid diagrams with static SVGs plus a fixture-backed real UI evidence PNG.
• Removed old README screenshot assets after repository-wide reference search confirmed they were unused.

New assets

• docs/assets/readme/preflight-logo.svg
• docs/assets/readme/preflight-hero.svg
• docs/assets/readme/preflight-workflow.svg
• docs/assets/readme/preflight-evidence.png
• docs/assets/readme/preflight-architecture.svg

Removed old assets

• docs/assets/preflight-home.png
• docs/assets/preflight-release-report.png
• docs/assets/preflight-receipt-inspector.png

Product behavior

Docs/assets only. No backend, frontend application code, API contracts, deployments, DNS, pricing, payment logic, npm publication, or ASP configuration changed.

Validation

• Backend: npm run typecheck && npm run build && npm test -- --run — 79 passed, 8 skipped.
• Web static: npm run lint && npm run build && npx tsc --noEmit — passed.
• Web browser: npx playwright test --reporter=list — 312 passed on final full rerun.
• CLI: npm run build && npm pack --dry-run --json — passed.
• CLI registry smoke: npx @vinaystwt/preflight-cli --help — passed.
• README local links: 13 local links checked, 0 broken.
• Badges/assets: CI and Shields badge URLs returned 200; SVGs parse at required dimensions; evidence PNG is 1400x900 sRGB.
• npm package metadata: npm view @vinaystwt/preflight-cli confirms version 0.1.0. npm.com HTML page returned 403 to curl in this environment, so package availability was verified through the registry API.

Render notes

• No Mermaid blocks remain in README.
• No old raw screenshot references remain in README.
• No Codex/Claude/orchestrator/private-artifact/obsolete-frontend wording remains in README.