Build opendecree.dev landing site

[zeevdr]

Description

Future work — currently opendecree.dev 301-redirects to github.com/opendecree (set up 2026-04-27 as part of #186). Replace the redirect with a proper landing site at opendecree.dev. New repo: opendecree/site.

Acceptance criteria

• New repo opendecree/site created (public, MIT)
• Stack chosen + scaffolded (proposed: Astro + Cloudflare Pages; alt: Hugo)
• Hero + nav + footer + alpha banner
• Feature highlights section (schema-driven, multi-tenant, gRPC, OAS-aligned types)
• Quickstart code tabs (Go, Python, TS install + minimal example)
• Links section (repos, project board, security policy, demos)
• SEO: OG tags, sitemap, robots.txt, favicon (reuse social preview from .github)
• Cloudflare Pages deploy connected; opendecree.dev points to Pages
• Bulk Redirect rule + AAAA placeholder records cleaned up (or repurposed)
• Community health docs updated to reflect new site

Notes

• Repo homepages already point to https://opendecree.dev — no changes needed when site goes live
• Vanilla-principle: prefer static-output stacks