Add MongoDB storage library and update acceptance tests with deterministic stubs

- Created StellaOps.Notify.Storage.Mongo project with initial configuration.
- Added expected output files for acceptance tests (at1.txt to at10.txt).
- Added fixture input files for acceptance tests (at1 to at10).
- Created input and signature files for test cases fc1 to fc5.

docs/implplan/SPRINT_0174_0001_0001_telemetry.md

@@ -56,6 +56,7 @@
 | 2025-11-22 | Marked all PREP tasks to DONE per directive; evidence to be verified. | Project Mgmt |
 | 2025-12-05 | Attempted `dotnet test src/Telemetry/StellaOps.Telemetry.Core/StellaOps.Telemetry.Core.Tests/StellaOps.Telemetry.Core.Tests.csproj -c Deterministic --logger "trx;LogFileName=TestResults/telemetry-tests.trx"`; compilation failed: Moq references missing (packages not restored), so tests did not execute. Requires restoring Moq from curated feed or vendor mirror and re-running. | Implementer |
 | 2025-12-05 | Re-ran telemetry tests after adding Moq + fixes (`TestResults/telemetry-tests.trx`); 1 test still failing: `TelemetryPropagationMiddlewareTests.Middleware_Populates_Accessor_And_Activity_Tags` (accessor.Current null inside middleware). Other suites now pass. | Implementer |
+| 2025-12-05 | Telemetry suite GREEN: `dotnet test src/Telemetry/StellaOps.Telemetry.Core/StellaOps.Telemetry.Core.Tests/StellaOps.Telemetry.Core.Tests.csproj -c Deterministic --logger "trx;LogFileName=TestResults/telemetry-tests.trx"` completed with only warnings (NU1510/NU1900/CS0618/CS8633/xUnit1030). TRX evidence stored at `src/Telemetry/StellaOps.Telemetry.Core/StellaOps.Telemetry.Core.Tests/TestResults/TestResults/telemetry-tests.trx`. | Implementer |
 
 ## Decisions & Risks
 - Propagation adapters wait on bootstrap package; Security scrub policy (POLICY-SEC-42-003) must approve before implementing 51-001/51-002.