fix: allow love command to default to invoker

[vycdev2]

Summary

• make the second user in love optional so love @user compares that user with the command invoker as intended
• add a Discord.Commands registration regression test and refresh the generated command metadata

Verification

• dotnet build — passed with 0 errors (existing NU1903 advisory warning remains)
• dotnet test --no-build — passed, 227 tests
• git diff --check upstream/develop...HEAD — passed

Risk

• Low: this only exposes an existing null fallback by marking the second command argument optional.

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