Add Orleans integration tests for orchestration and checkpoint-resume

[KSemenenko]

Problem

The embedded host and multi-agent workflow model need dedicated Orleans-level verification before they can be trusted.

Scope

• Track Orleans integration coverage for grain flows, orchestration, and checkpoint-resume behavior
• Cover traffic-policy and session-resume expectations
• Keep tests aligned with the embedded-host architecture

Out of scope

• UI shell verification
• Provider toolchain installation checks

Implementation notes

• Use real Orleans integration tests for runtime boundaries
• Ensure orchestration and resume behavior are tested through the runtime, not only by unit seams
• Align with Orleans.Graph planning

Definition of Done

• The issue defines the Orleans integration scenarios the product must prove
• Later implementation can add the right integration harness instead of guessing

Verification

• Review the issue against the runtime epic and AGENTS testing policy

Dependencies

• Parent epic: [Epic] Expand automated validation for the control-plane product #21
• Related epic: [Epic] Add the embedded agent runtime host to the Uno desktop app #12