Add a compact visible-loop diagram to README

[wcqxgjy6d8-pixel]

Goal

Add a compact text or Mermaid diagram near the README entry path that shows the VALP loop from publish to audit.

Why this helps

New readers should see the control-system shape before reading the full spec.

Scope

• Keep it runtime-neutral.
• Do not introduce new protocol semantics.
• Link to docs/visual-flow.md if useful.

Verification

• Run scripts/verify-examples.sh, or explain if this is docs-only and not run.