fix: honor stock update cancellation

[vycdev2]

Summary

• propagate the Quartz cancellation token through the stock lookup, batch saves, and inter-batch delay
• stop between individual stock updates when shutdown or an interrupt is requested
• add a regression test proving a pre-cancelled scheduler run exits with cancellation

Verification

• dotnet build — passed with 0 errors (2 existing NU1903 warnings for SQLitePCLRaw.lib.e_sqlite3 2.1.6)
• dotnet test --no-build --logger "console;verbosity=minimal" — passed: 429, skipped: 1
• dotnet test Morpheus.Tests/Morpheus.Tests.csproj --filter "FullyQualifiedName~StockUpdateJobTests" --logger "console;verbosity=minimal" — passed: 1
• git diff --check upstream/develop...HEAD — passed

Risk

• Low: the change only affects cancellation handling in the stock update job; normal update ordering and calculations are unchanged.

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