Adaptive themed diagrams

The five Context Rails and role-lens diagram families now have one canonical Mermaid source under the documentation tree, explicit manifests, adaptive fallback SVGs, and host SVGs. Every adaptive custom-property reference includes a concrete light fallback. The Next.js site receives only generated artifacts, and a client boot component upgrades marked images only after the sanitized host file loads.

The Git/Vercel topology was redrawn from its Excalidraw model while retaining the Excalidraw source and fixed light/dark exports. The tracked React component architecture remains semantically useful because its documented component and store paths still exist, so it now participates in the same manifest and artifact checks. The five original hand-authored HCI SVGs remain available in Git history; their invalid control characters made them unsuitable as fixed assets.