feat: public Skillbench release

[alexrett]

Outcome

• ships the public npm package metadata, MIT license, contributor and security docs
• adds PR/main CI, Pages deployment, trusted npm publishing, and five release binaries
• adds the full static GitHub Pages site with interactive TUI, workflow, docs, comparison, and quickstart sections
• adds dependency update automation and release notes

Local evidence

• bun run check — 15 tests pass
• bun run site:check — links, anchors, and local assets pass
• bun audit --audit-level high — no vulnerabilities
• npm pack --dry-run — expected four-file package
• clean-prefix global npm install — skillbench --version returns 0.3.0
• binary smoke — registry doctor passes for two packages
• browser QA — desktop 1536×1024 and mobile 390×844, no document overflow or console errors

Release follow-up

After merge: deploy Pages, publish the initial npm package, configure npm trusted publishing, tag the release, and verify installation from the public registry.

[Copilot]

Pull request overview

This PR prepares Skillbench for its first public release by adding public-facing documentation and a static GitHub Pages site, and by introducing CI/release automation for publishing and binaries.

Changes:

• Adds a full static website (HTML/CSS/JS) plus manifest/robots/sitemap and social assets under site/.
• Adds automated site validation (scripts/check-site.ts) and wires it into CI/Pages/release workflows.
• Updates packaging + project metadata (MIT license, npm metadata, contributing/security docs) and adds release automation (CI, Pages deploy, release + binaries, Dependabot).

Reviewed changes

Copilot reviewed 19 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
site/styles.css	Adds complete styling for the public static site.
site/index.html	Adds the static landing page markup and interactive sections.
site/script.js	Adds client-side behavior (copy buttons, nav toggle, interactive previews).
site/site.webmanifest	Adds PWA manifest metadata and icon reference.
site/robots.txt	Enables crawling and points to sitemap.
site/sitemap.xml	Adds sitemap for the Pages site root.
site/assets/og-skillbench.svg	Adds OG image source asset (SVG variant).
site/assets/favicon.svg	Adds SVG favicon.
scripts/check-site.ts	Adds a Bun script to validate required HTML, anchors, and local assets.
.github/workflows/ci.yml	Adds PR/main CI (typecheck/tests/audit/package/site + binary smoke).
.github/workflows/pages.yml	Adds Pages deployment workflow for the static site.
.github/workflows/release.yml	Adds tag-driven release workflow for validation, binaries, npm publish, and GitHub release.
package.json	Publishes package metadata, adds site scripts, includes LICENSE, sets MIT license + publish config.
README.md	Rewrites README for public usage, workflows, and release model.
LICENSE	Adds MIT license text.
SECURITY.md	Adds vulnerability reporting + safety guidance.
CONTRIBUTING.md	Adds contribution guidance and PR invariants.
CHANGELOG.md	Adds initial changelog entry for 0.3.0.
.github/pull_request_template.md	Adds PR template with evidence checklist + invariants.
.github/dependabot.yml	Adds Dependabot config for npm + GitHub Actions.
.github/CODEOWNERS	Sets repository-wide code ownership.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.