Add new features and tests for AirGap and Time modules

- Introduced `SbomService` tasks documentation.
- Updated `StellaOps.sln` to include new projects: `StellaOps.AirGap.Time` and `StellaOps.AirGap.Importer`.
- Added unit tests for `BundleImportPlanner`, `DsseVerifier`, `ImportValidator`, and other components in the `StellaOps.AirGap.Importer.Tests` namespace.
- Implemented `InMemoryBundleRepositories` for testing bundle catalog and item repositories.
- Created `MerkleRootCalculator`, `RootRotationPolicy`, and `TufMetadataValidator` tests.
- Developed `StalenessCalculator` and `TimeAnchorLoader` tests in the `StellaOps.AirGap.Time.Tests` namespace.
- Added `fetch-sbomservice-deps.sh` script for offline dependency fetching.

tests/AirGap/StellaOps.AirGap.Importer.Tests/BundleImportPlannerTests.cs

@@ -0,0 +1,40 @@
+using StellaOps.AirGap.Importer.Contracts;
+using StellaOps.AirGap.Importer.Planning;
+
+namespace StellaOps.AirGap.Importer.Tests;
+
+public class BundleImportPlannerTests
+{
+    [Fact]
+    public void ReturnsFailureWhenBundlePathMissing()
+    {
+        var planner = new BundleImportPlanner();
+        var result = planner.CreatePlan(string.Empty, TrustRootConfig.Empty("/tmp"));
+
+        Assert.False(result.InitialState.IsValid);
+        Assert.Equal("bundle-path-required", result.InitialState.Reason);
+    }
+
+    [Fact]
+    public void ReturnsFailureWhenTrustRootsMissing()
+    {
+        var planner = new BundleImportPlanner();
+        var result = planner.CreatePlan("bundle.tar", TrustRootConfig.Empty("/tmp"));
+
+        Assert.False(result.InitialState.IsValid);
+        Assert.Equal("trust-roots-required", result.InitialState.Reason);
+    }
+
+    [Fact]
+    public void ReturnsDefaultPlanWhenInputsProvided()
+    {
+        var planner = new BundleImportPlanner();
+        var trust = new TrustRootConfig("/tmp/trust.json", new[] { "abc" }, new[] { "ed25519" }, null, null, new Dictionary<string, byte[]>());
+
+        var result = planner.CreatePlan("bundle.tar", trust);
+
+        Assert.True(result.InitialState.IsValid);
+        Assert.Contains("verify-dsse-signature", result.Steps);
+        Assert.Equal("bundle.tar", result.Inputs["bundlePath"]);
+    }
+}