Deploy coverage reports to GitHub Pages

[Copilot]

Coverage reports were generated in CI but only available as downloadable artifacts. They now deploy to GitHub Pages for direct browser viewing.

Changes

README.md

• Added coverage badge linking to https://pgit.github.io/anyhttp/coverage/

.github/workflows/release.yml (coverage job)

• Added pages: write and id-token: write permissions
• Created pages directory structure: pages/coverage/
• Deploy to GitHub Pages on master branch pushes via actions/upload-pages-artifact@v3 and actions/deploy-pages@v4
• Artifact upload preserved for all runs (PRs included)

Deployment Behavior

# Deploys only on master branch pushes, not PRs
if: github.ref == 'refs/heads/master' && github.event_name == 'push'

On merge to master, coverage will be viewable at https://pgit.github.io/anyhttp/coverage/

Repository Configuration

Requires GitHub Pages enabled with source set to "GitHub Actions" (Settings → Pages).

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