fix: reject zero owner IDs

[vycdev2]

Summary

• reject OWNER_ID=0 as unconfigured instead of treating it as a valid Discord user ID
• cover zero-valued owner configuration with a regression case

Verification

• dotnet test --no-restore --filter 'FullyQualifiedName~AdministratorModuleTests.TryParseOwnerId_RejectsMissingOrInvalidValues' — passed (5/5)
• dotnet build — passed with 0 warnings and 0 errors
• dotnet test --no-build — passed (608 passed, 3 skipped)
• git diff --check — passed

Risk

• Low. The change only rejects the reserved zero snowflake, which can never identify a Discord user.

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