Add AgentPass action-boundary infographic

[dinpd]

Closes #65

Summary

• add a project-owned 1672×941 AgentPass action-boundary infographic under docs/
• distinguish current stateful runtime control and intent assurance from the causal-observability roadmap
• embed the image after the README's two-plane introduction with descriptive alt text
• retain the existing enterprise-managed MCP authorization diagram

Acceptance evidence

• Visually inspected the full-resolution image and a 900×506 README-width rendering for hierarchy, contrast, cropping, spelling, and roadmap labeling.
• OCR recovered the title, execution flow, current controls, intent assurance, roadmap label, and OpenTelemetry terminology; ambiguous OCR glyphs were checked visually against the rendered asset.
• Verified the PNG is non-empty RGB image data at 1672×941.
• Verified all 34 relative README link/image targets resolve locally.
• Verified the new embed and existing MCP authorization image are both present.
• git diff --check passes.

Security and scope review

• Documentation-only; no runtime, dependency, permission, or data-flow changes.
• Targeted scans of the README and PNG strings found no common credential patterns.
• Manually reviewed the complete two-file diff for issue scope.
• The PNG retains OpenAI C2PA provenance metadata and contains no personal project data.
• No repository-native documentation or link-check workflow is configured; the local path verifier above covers relative README targets.