Explain hosted sharing and refine homepage animation

[callumalpass]

Changes

• Add a hosted-sharing homepage stage with viewer/editor roles and update Connect/Editor copy.
• Fit and wrap canvas labels responsively; clarify the final scene with removed app access and unchanged records.
• Preserve the site-owned animation during source synchronization instead of overwriting it with the Connect prototype.
• Run nine homepage regression tests in CI and production deployment.

Validation

• Approved development preview at https://mdbase-dev.pages.dev
• Chromium checks across six viewport widths, dark mode, and reduced motion
• Homepage tests, Astro checks, production build, specification import, and local link checks pass
• Based on current main, preserving beta.98 downloads and existing release automation

User approved production deployment.