fix: honor UBI job cancellation

[vycdev2]

Summary

• pass the Quartz cancellation token through the UBI distribution transaction and database operations
• propagate cancellation instead of converting it into a successful error result
• add a regression test covering cancellation through the scheduled job entry point

Verification

• dotnet build --no-restore — passed: 0 errors (1 existing SQLite package vulnerability warning)
• dotnet test --no-restore --filter "FullyQualifiedName~UbiJobTests" --logger "console;verbosity=minimal" — passed: 1/1
• dotnet test --no-restore --logger "console;verbosity=minimal" — passed: 429, skipped: 1, failed: 0
• git diff --check upstream/develop...HEAD — passed

Risk

• Low — the change only affects shutdown/interruption behavior for the scheduled UBI job; normal callers retain the default non-cancelable token.

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