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.

src/ExportCenter/StellaOps.ExportCenter/StellaOps.ExportCenter.Core/Services/TimelineEvidenceClient.cs

@@ -0,0 +1,25 @@
+using StellaOps.TimelineIndexer.Core.Abstractions;
+using StellaOps.TimelineIndexer.Core.Models;
+
+namespace StellaOps.ExportCenter.Core.Services;
+
+/// <summary>
+/// Thin client surface to fetch timeline evidence linkage for export runs.
+/// Uses manifest fallback when evidence payload omits explicit manifest URI.
+/// </summary>
+public sealed class TimelineEvidenceClient
+{
+    private readonly ITimelineQueryService _queryService;
+
+    public TimelineEvidenceClient(ITimelineQueryService queryService)
+    {
+        _queryService = queryService;
+    }
+
+    public Task<TimelineEvidenceView?> GetEvidenceAsync(string tenantId, string eventId, CancellationToken cancellationToken = default)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(eventId);
+        return _queryService.GetEvidenceAsync(tenantId, eventId, cancellationToken);
+    }
+}

src/ExportCenter/StellaOps.ExportCenter/StellaOps.ExportCenter.Core/StellaOps.ExportCenter.Core.csproj

@@ -14,4 +14,8 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.0-rc.2.25502.107" />
   </ItemGroup>
-</Project>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\TimelineIndexer\StellaOps.TimelineIndexer\StellaOps.TimelineIndexer.Core\StellaOps.TimelineIndexer.Core.csproj" />
+  </ItemGroup>
+</Project>

src/ExportCenter/StellaOps.ExportCenter/StellaOps.ExportCenter.Infrastructure/StellaOps.ExportCenter.Infrastructure.csproj

@@ -10,6 +10,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\StellaOps.ExportCenter.Core\StellaOps.ExportCenter.Core.csproj" />
+    <ProjectReference Include="..\..\..\TimelineIndexer\StellaOps.TimelineIndexer\StellaOps.TimelineIndexer.Core\StellaOps.TimelineIndexer.Core.csproj" />
   </ItemGroup>
 
   <ItemGroup>

src/ExportCenter/StellaOps.ExportCenter/StellaOps.ExportCenter.WebService/StellaOps.ExportCenter.WebService.csproj

@@ -17,5 +17,6 @@
     <ProjectReference Include="..\..\..\Authority\StellaOps.Authority\StellaOps.Auth.ServerIntegration\StellaOps.Auth.ServerIntegration.csproj" />
     <ProjectReference Include="..\..\..\Authority\StellaOps.Authority\StellaOps.Auth.Abstractions\StellaOps.Auth.Abstractions.csproj" />
     <ProjectReference Include="..\..\..\AirGap\StellaOps.AirGap.Policy\StellaOps.AirGap.Policy\StellaOps.AirGap.Policy.csproj" />
+    <ProjectReference Include="..\..\..\TimelineIndexer\StellaOps.TimelineIndexer\StellaOps.TimelineIndexer.Core\StellaOps.TimelineIndexer.Core.csproj" />
   </ItemGroup>
 </Project>