Add multi-host boot consistency smoke test for installed agents

[curtisman]

Summary

Add a smoke/integration scenario that boots the shell, agentServer, and web API host paths against one fresh instance directory and verifies they observe the same installed-agent state.

Background

The per-host wiring is covered by build/type-check and unit tests around the shared installed-agent records, but no single test boots all host entry points against the same agents.json / install-source config and verifies consistent visibility.

Suggested Coverage

• create a fresh instance directory with installed-agent state
• boot shell, agentServer, and API host paths against that instance directory
• verify all hosts see the same installed agents and source-derived state
• include restart/reload behavior if the smoke harness can do so cheaply

Source

Deferred from PR #2611 review-log cleanup.