Show AML's agent action boundary as a live visual path

[aruintelligence]

Visual changes

• Add a repository-native SVG story in the README: a proposed message to an unlisted destination is blocked by the host's exact rule before any tool callback.
• Add a four-stage visual path to the Action Boundary Lab. It updates from the same local plan and simulated outcome as the detailed report: proposal → host policy → simulated approval → rehearsal outcome.
• Keep labels explicit about simulation, stale approval, unknown callback outcome, and no live tool or human approval.

Verification

• SVG rendered and visually inspected at 1200×380; XML parsed successfully.
• node --check docs/action-lab.js
• node --test test/action-lab.test.js test/action-boundary-guarded-tool.test.js test/action-boundary-challenge.test.js

The browser lab remains a project-authored rehearsal and does not call a real tool.