fix: refresh guild names after server renames

[vycdev2]

Summary

• refresh the persisted Discord guild name when an existing server is renamed
• add a SQLite regression test covering both the returned and persisted guild record

Verification

• dotnet test Morpheus.Tests/Morpheus.Tests.csproj --no-restore --filter FullyQualifiedName~GuildServiceTests — passed (1/1)
• dotnet build --no-restore — passed with the existing SQLitePCLRaw vulnerability warning
• dotnet test --no-restore — 298 passed, 2 failed because this runner uses invariant globalization and cannot load tr-TR; the unrelated portable-culture fix is already tracked in test: skip unavailable culture regression #81
• git diff --check — passed

Risk

• Low: the change only writes when a stored guild name differs, matching the existing channel-name refresh behavior.

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