feat(kms): Implement file-backed key management commands and handlers

- Added `kms export` and `kms import` commands to manage file-backed signing keys.
- Implemented `HandleKmsExportAsync` and `HandleKmsImportAsync` methods in CommandHandlers for exporting and importing key material.
- Introduced KmsPassphrasePrompt for secure passphrase input.
- Updated CLI architecture documentation to include new KMS commands.
- Enhanced unit tests for KMS export and import functionalities.
- Updated project references to include StellaOps.Cryptography.Kms library.
- Marked KMS interface implementation and CLI support tasks as DONE in the task board.

NuGet.config

@@ -34,11 +34,12 @@
       <package pattern="System.Memory" />
       <package pattern="System.Runtime.CompilerServices.Unsafe" />
     </packageSource>
-    <packageSource key="dotnet-public">
-      <package pattern="Microsoft.Extensions.*" />
-      <package pattern="Microsoft.AspNetCore.*" />
-      <package pattern="Microsoft.Data.Sqlite" />
-    </packageSource>
+    <packageSource key="dotnet-public">
+      <package pattern="Microsoft.Extensions.*" />
+      <package pattern="Microsoft.AspNetCore.*" />
+      <package pattern="Microsoft.Data.Sqlite" />
+      <package pattern="System.Diagnostics.*" />
+    </packageSource>
     <packageSource key="nuget.org">
       <package pattern="*" />
     </packageSource>