Phase 3C: Deployment pipeline & Store-and-Forward engine

Deployment Manager (WP-1–8, WP-16):
- DeploymentService: full pipeline (flatten→validate→send→track→audit)
- OperationLockManager: per-instance concurrency control
- StateTransitionValidator: Enabled/Disabled/NotDeployed transition matrix
- ArtifactDeploymentService: broadcast to all sites with per-site results
- Deployment identity (GUID + revision hash), idempotency, staleness detection
- Instance lifecycle commands (disable/enable/delete) with deduplication

Store-and-Forward (WP-9–15):
- StoreAndForwardStorage: SQLite persistence, 3 categories, no max buffer
- StoreAndForwardService: fixed-interval retry, transient-only buffering, parking
- ReplicationService: async best-effort to standby (fire-and-forget)
- Parked message management (query/retry/discard from central)
- Messages survive instance deletion, S&F drains on disable

620 tests pass (+79 new), zero warnings.

tests/ScadaLink.DeploymentManager.Tests/DeploymentComparisonTests.cs

@@ -0,0 +1,37 @@
+namespace ScadaLink.DeploymentManager.Tests;
+
+/// <summary>
+/// WP-8: Tests for deployed vs template-derived state comparison.
+/// </summary>
+public class DeploymentComparisonTests
+{
+    [Fact]
+    public void DeploymentComparisonResult_MatchingHashes_NotStale()
+    {
+        var result = new DeploymentComparisonResult(
+            1, "sha256:abc", "sha256:abc", false, DateTimeOffset.UtcNow);
+
+        Assert.False(result.IsStale);
+        Assert.Equal("sha256:abc", result.DeployedRevisionHash);
+        Assert.Equal("sha256:abc", result.CurrentRevisionHash);
+    }
+
+    [Fact]
+    public void DeploymentComparisonResult_DifferentHashes_IsStale()
+    {
+        var result = new DeploymentComparisonResult(
+            1, "sha256:old", "sha256:new", true, DateTimeOffset.UtcNow);
+
+        Assert.True(result.IsStale);
+        Assert.NotEqual(result.DeployedRevisionHash, result.CurrentRevisionHash);
+    }
+
+    [Fact]
+    public void DeploymentComparisonResult_ContainsDeployedTimestamp()
+    {
+        var deployedAt = new DateTimeOffset(2026, 3, 16, 12, 0, 0, TimeSpan.Zero);
+        var result = new DeploymentComparisonResult(1, "h1", "h2", true, deployedAt);
+
+        Assert.Equal(deployedAt, result.DeployedAt);
+    }
+}