[Epic] Add the embedded agent runtime host to the Uno desktop app

[KSemenenko]

Problem

dotPilot needs a tracked epic for the embedded runtime host that will turn the desktop app into the local control plane for session orchestration.

Scope

• Track Orleans host embedding, core grains, Agent Framework integration, traffic policy, and durable session state
• Keep the v1 runtime local-first and desktop-embedded

Out of scope

• Remote worker hosting and distributed fleet deployment
• Product UI implementation details outside runtime integration

Planned child issues

• Embed an Orleans silo and register the core grains
• Integrate Microsoft Agent Framework as the orchestration runtime
• Define grain traffic policy with ManagedCode.Orleans.Graph
• Implement session persistence, replay, checkpointing, and resume

Definition of Done

• The runtime foundation issues exist and reference this epic
• The epic states the local-first embedded-host goal unambiguously

Verification

• Child issues reference this epic
• Issue scope remains runtime-focused and does not drift into unrelated UI work