Fix backend chat recovery version domain

[AbigailDeng]

Problem

Create recovery reads stateVersion from the ChatTurnHistoryDeliveryGAgent recovery resource. The Workflow Application copied that delivery-resource version into WorkflowChatContext.StateVersion, whose SSE contract represents a ChatConversationGAgent watermark. Distinct actor version domains could therefore be conflated.

Backend solution

• Preserve the delivery version on the recovery read model for recovery-resource freshness.
• Do not copy that version into recovered WorkflowChatContext; recovered creates use the context default 0 until Conversation detail exposes its authoritative watermark.
• Add a regression using delivery version 4 and expected Conversation context version 0.
• Document the recovery-response and SSE version-domain contracts.

Scope

This PR contains only backend implementation, backend tests, and canonical contract documentation. It has no frontend files. The independently effective frontend hardening is tracked in #3067.

Validation

• /Users/abigaildeng/.dotnet/dotnet test test/Aevatar.Workflow.Application.Tests/Aevatar.Workflow.Application.Tests.csproj --nologo --no-restore (457 passed)
• bash tools/ci/test_stability_guards.sh
• bash tools/ci/projection_state_version_guard.sh
• bash tools/docs/lint.sh (83 files, 0 errors)

[Abigail940404]

Closing per scope decision: the user-facing History save was not confirmed bug is caused by the frontend treating create recovery/context versions as Conversation watermarks. Frontend PR #3067 is independently effective against the existing backend contract, so this backend change is not required for the fix and should not block the frontend release.

[AbigailDeng]

Closing per scope decision: the user-facing History save was not confirmed bug is caused by the frontend treating create recovery/context versions as Conversation watermarks. Frontend PR #3067 is independently effective against the existing backend contract, so this backend change is not required for the fix and should not block the frontend release.