[codex] Add dashboard read models

[cody257]

Summary

• Add a backend-only DashboardReadModelService for frontend-ready state.
• Expose module cards, pending Tune approvals, recent ledger events, and dashboard summary state.
• Keep the service read-only over ModuleStatusService and IBlackboardStore; no Tune execution or module jobs are run.
• Add focused tests for module cards, pending proposal filtering, recent event ordering, and summary counts.

Validation

• dotnet test .\tests\AppLens.Backend.Tests\AppLens.Backend.Tests.csproj --filter DashboardReadModelServiceTests: 3 passed, 0 failed.
• dotnet test .\AppLensDesktop.sln: 47 passed, 0 failed.
• dotnet build .\AppLensDesktop.sln: succeeded with 0 warnings and 0 errors.
• git diff --cached --check: passed.

Notes

• Backend only. No frontend changes.
• No live system-changing jobs were run.