Implement session persistence, replay, checkpointing, and resume

[KSemenenko]

Problem

Operators need durable session state so long-running and approval-gated work can survive restarts and be replayed later.

Scope

• Track transcript persistence, artifact persistence, replay, export, checkpointing, and resume flows
• Cover both normal session resume and approval-gated pause-resume behavior

Out of scope

• Provider-specific replay logic that bypasses the shared session model
• UI polish outside the required persistence and replay capabilities

Implementation notes

• Align the planned persistence model with Agent Framework session and workflow checkpoints
• Keep replay exportable and auditable
• Make the issue applicable to coding and non-coding sessions

Definition of Done

• The issue defines what must be persisted, replayed, checkpointed, and resumed
• The approval and restart scenarios are explicitly covered

Verification

• Review the issue against the feature spec session lifecycle and audit expectations

Dependencies

• Parent epic: [Epic] Add the embedded agent runtime host to the Uno desktop app #12
• Depends on: Integrate Microsoft Agent Framework as the orchestration runtime