fix: attribute pins to original message author

[vycdev2]

Summary

• attribute pin embed titles to the author of the referenced message instead of the moderator invoking pin
• add regression coverage for pin title formatting

Verification

• dotnet test Morpheus.Tests/Morpheus.Tests.csproj --filter FullyQualifiedName~UtilityModuleTests --logger console;verbosity=minimal — passed: 11/11
• dotnet build — passed: 0 errors (2 existing package-vulnerability warnings)
• dotnet test — 298/300 passed; the two failures are existing tr-TR cases unavailable in this runner's globalization-invariant mode
• git diff --check upstream/develop...HEAD — passed

Risk

• Low — the change only corrects display attribution in pin embeds and does not alter permissions, persistence, or command flow.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.