Improve discoverability, SEO, and contributor onboarding

[MrAlfak]

Goal

Make httpCode easier to discover, understand, share, star, and contribute to without weakening its technical quality.

Discoverability

• Reworks README into a fast-scanning project landing page with real CI/release/stars/forks/license badges, clearer positioning, use cases, quick start, and a lightweight star CTA.
• Expands npm/Python package metadata and searchable keywords.
• Adds Code of Conduct, Support, Roadmap, Citation metadata, issue forms, and a pull request template.
• Adds contribution-friendly entry points for bugs, features, and source-backed data corrections.

Web SEO and sharing

• Adds OpenGraph, Twitter, canonical, robots, keywords, JSON-LD, favicon, and web-app manifest metadata.
• Generates per-status SEO metadata, sitemap.xml, and robots.txt for static builds.
• Adds a GitHub Star CTA to the web explorer.

GitHub Pages readiness

• Fixes absolute-path assumptions so the app can run under /httpCode/.
• Adds a GitHub Pages deployment workflow using a repository base path.
• Keeps Pages deployment manual until repository Pages is enabled in Settings → Pages → Source: GitHub Actions.

Validation requested

Existing CI should cover Python tests/data validation plus Node syntax/build/audit. The Pages workflow is intentionally workflow_dispatch only until Pages is enabled in repository settings.