AB#3268: add journal drift verb

[PolyphonyRequiem]

Summary

• add Phase 4 polyphony journal drift command wiring and result model
• project expected journal resource state and diff it with read-only observers
• cover the new verb with projection, command, DI, and JSON contract tests

Testing

• dotnet build src\Polyphony\Polyphony.csproj -c Release
• dotnet build tests\Polyphony.Tests\Polyphony.Tests.csproj -c Release
• dotnet test tests\Polyphony.Tests -c Release --filter "FullyQualifiedNameJournalDrift|FullyQualifiedNameJsonOutputContractTests|FullyQualifiedNamePolyphonyServiceRegistrationTests|FullyQualifiedNameVerbCoverageTests"
• dotnet test tests\Polyphony.Tests --no-build -c Release --filter "FullyQualifiedNameJournal|FullyQualifiedNamePolyphonyServiceRegistrationTests|FullyQualifiedName~VerbCoverageTests"

Notes

• full-suite validation is still blocked by two unrelated issues in this worktree: missing artifacts\verb-output-schemas.json and LifecycleRouterScriptTests failing to launch pwsh

AB#3268