Add Kova Engine technical preview

[ogyrec-o]

What changed

• adds /projects/kova/ as a native Chirpy page
• uses the existing site layout, typography, content width, code blocks, tables, image handling, and table of contents
• adds no custom layout, CSS, or JavaScript
• removes the earlier badge-like status row and fake CTA link row
• replaces the custom architecture SVG with a native text diagram, boundary table, and concise design rules
• reduces colored callout boxes in favor of normal prose notes
• adds a small Kova link and summary to the existing Projects tab
• documents the current Camera Orbit, Basic 3D, and Basic 2D examples using excerpts checked against the private engine repository
• keeps minimal illustrated placeholders that can be replaced with real captures later

Review note

This PR is intentionally left as a draft and is not merged. The previous custom landing-page implementation was removed from main before this branch was created.

Current diff

• one Markdown project page
• one small Projects tab edit
• three visible demo placeholders
• one social preview image
• no page-specific CSS, JavaScript, or layout files