feat(audit): Apply TreatWarningsAsErrors=true to 160+ production csproj files

Sprint: SPRINT_20251229_049_BE_csproj_audit_maint_tests
Tasks: AUDIT-0001 through AUDIT-0147 APPLY tasks (approved decisions 1-9)

Changes:
- Set TreatWarningsAsErrors=true for all production .NET projects
- Fixed nullable warnings in Scanner.EntryTrace, Scanner.Evidence,
  Scheduler.Worker, Concelier connectors, and other modules
- Injected TimeProvider/IGuidProvider for deterministic time/ID generation
- Added path traversal validation in AirGap.Bundle
- Fixed NULL handling in various cursor classes
- Third-party GostCryptography retains TreatWarningsAsErrors=false (preserves original)
- Test projects excluded per user decision (rejected decision 10)

Note: All 17 ACSC connector tests pass after snapshot fixture sync

src/Scanner/__Libraries/StellaOps.Scanner.Evidence/FuncProofTransparencyService.cs

@@ -310,6 +310,11 @@ public sealed class FuncProofTransparencyService : IFuncProofTransparencyService
         HttpResponseMessage? response = null;
         Exception? lastException = null;
 
+        if (string.IsNullOrWhiteSpace(opts.RekorUrl))
+        {
+            throw new InvalidOperationException("RekorUrl must be configured for transparency log submission");
+        }
+
         for (var attempt = 0; attempt < opts.RetryCount; attempt++)
         {
             try
@@ -353,7 +358,7 @@ public sealed class FuncProofTransparencyService : IFuncProofTransparencyService
             throw new HttpRequestException($"Failed to submit to Rekor after {opts.RetryCount} attempts: {errorMsg}");
         }
 
-        return await ParseRekorResponseAsync(response, ct).ConfigureAwait(false);
+        return await ParseRekorResponseAsync(response!, ct).ConfigureAwait(false);
     }
 
     private static object BuildRekorEntry(DsseEnvelope envelope)

src/Scanner/__Libraries/StellaOps.Scanner.Evidence/StellaOps.Scanner.Evidence.csproj

@@ -5,7 +5,7 @@
     <LangVersion>preview</LangVersion>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
-    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />