Add property-based tests for SBOM/VEX document ordering and Unicode normalization determinism

- Implement `SbomVexOrderingDeterminismProperties` for testing component list and vulnerability metadata hash consistency.
- Create `UnicodeNormalizationDeterminismProperties` to validate NFC normalization and Unicode string handling.
- Add project file for `StellaOps.Testing.Determinism.Properties` with necessary dependencies.
- Introduce CI/CD template validation tests including YAML syntax checks and documentation content verification.
- Create validation script for CI/CD templates ensuring all required files and structures are present.

src/Cli/__Libraries/StellaOps.Cli.Plugins.Vex/StellaOps.Cli.Plugins.Vex.csproj

@@ -0,0 +1,32 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <!--
+    StellaOps.Cli.Plugins.Vex.csproj
+    Sprint: SPRINT_20251226_011_BE_auto_vex_downgrade
+    Task: AUTOVEX-15 - CLI command: stella vex auto-downgrade
+    Description: CLI plugin for VEX management and auto-downgrade commands
+  -->
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <LangVersion>preview</LangVersion>
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
+    <PluginOutputDirectory>$([System.IO.Path]::GetFullPath('$(MSBuildThisFileDirectory)..\..\plugins\cli\StellaOps.Cli.Plugins.Vex\'))</PluginOutputDirectory>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\StellaOps.Cli\StellaOps.Cli.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Spectre.Console" Version="0.48.0" />
+  </ItemGroup>
+
+  <Target Name="CopyPluginBinaries" AfterTargets="Build">
+    <MakeDir Directories="$(PluginOutputDirectory)" />
+    <Copy SourceFiles="$(TargetDir)$(TargetFileName)" DestinationFolder="$(PluginOutputDirectory)" />
+    <Copy SourceFiles="$(TargetDir)$(TargetName).pdb"
+          DestinationFolder="$(PluginOutputDirectory)"
+          Condition="Exists('$(TargetDir)$(TargetName).pdb')" />
+  </Target>
+</Project>