Local site preview, build, and Mermaid support

Everlock now has a clearer path for working on project sites locally.

What changed

• Mermaid diagrams are supported as a general backend-site-http capability instead of a one-off website customization.
• The CLI now has explicit command routing with everlock serve and everlock version.
• Local site tooling is being added under everlock site, including preview and static build flows that reuse the same site engine as deployed serving.

Why this matters

The public project site should be easy to edit, preview, and understand without needing a deployed instance first. That is especially useful for documentation-heavy open source work where contributors need tight feedback loops.

Direction

The goal is to keep local preview and deployed behavior aligned, so the same Markdown rendering, shortcodes, templates, Mermaid handling, and routing rules apply in both places.