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/__Libraries/StellaOps.Cryptography.Plugin.CryptoPro/StellaOps.Cryptography.Plugin.CryptoPro.csproj

@@ -5,7 +5,7 @@
     <LangVersion>preview</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
-    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <!-- Exclude vendored fork files from this project (they compile via their own csproj) -->
     <DefaultItemExcludes>$(DefaultItemExcludes);third_party\**\*</DefaultItemExcludes>
   </PropertyGroup>

src/__Libraries/StellaOps.Cryptography.Plugin.CryptoPro/third_party/AlexMAS.GostCryptography/Source/GostCryptography/GostCryptography.csproj

@@ -13,6 +13,7 @@
     <AssemblyVersion>$(GostCryptographyVersion).0</AssemblyVersion>
     <FileVersion>$(GostCryptographyVersion).0</FileVersion>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <!-- Third-party library - preserve original warning level -->
     <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
   </PropertyGroup>