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/ArtifactDeploymentServiceTests.cs

@@ -0,0 +1,85 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using NSubstitute;
+using ScadaLink.Commons.Entities.Sites;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Interfaces.Services;
+using ScadaLink.Commons.Messages.Artifacts;
+using ScadaLink.Communication;
+
+namespace ScadaLink.DeploymentManager.Tests;
+
+/// <summary>
+/// WP-7: Tests for system-wide artifact deployment.
+/// </summary>
+public class ArtifactDeploymentServiceTests
+{
+    private readonly ISiteRepository _siteRepo;
+    private readonly IDeploymentManagerRepository _deploymentRepo;
+    private readonly IAuditService _audit;
+
+    public ArtifactDeploymentServiceTests()
+    {
+        _siteRepo = Substitute.For<ISiteRepository>();
+        _deploymentRepo = Substitute.For<IDeploymentManagerRepository>();
+        _audit = Substitute.For<IAuditService>();
+    }
+
+    [Fact]
+    public async Task DeployToAllSitesAsync_NoSites_ReturnsFailure()
+    {
+        _siteRepo.GetAllSitesAsync().Returns(new List<Site>());
+
+        var service = CreateService();
+        var command = CreateCommand();
+
+        var result = await service.DeployToAllSitesAsync(command, "admin");
+
+        Assert.True(result.IsFailure);
+        Assert.Contains("No sites", result.Error);
+    }
+
+    [Fact]
+    public void SiteArtifactResult_ContainsSiteInfo()
+    {
+        var result = new SiteArtifactResult("site1", "Site One", true, null);
+        Assert.Equal("site1", result.SiteId);
+        Assert.Equal("Site One", result.SiteName);
+        Assert.True(result.Success);
+        Assert.Null(result.ErrorMessage);
+    }
+
+    [Fact]
+    public void ArtifactDeploymentSummary_CountsCorrectly()
+    {
+        var results = new List<SiteArtifactResult>
+        {
+            new("s1", "Site1", true, null),
+            new("s2", "Site2", false, "error"),
+            new("s3", "Site3", true, null)
+        };
+        var summary = new ArtifactDeploymentSummary("dep1", results, 2, 1);
+
+        Assert.Equal(2, summary.SuccessCount);
+        Assert.Equal(1, summary.FailureCount);
+        Assert.Equal(3, summary.SiteResults.Count);
+    }
+
+    private ArtifactDeploymentService CreateService()
+    {
+        var comms = new CommunicationService(
+            Options.Create(new CommunicationOptions()),
+            NullLogger<CommunicationService>.Instance);
+
+        return new ArtifactDeploymentService(
+            _siteRepo, _deploymentRepo, comms, _audit,
+            Options.Create(new DeploymentManagerOptions()),
+            NullLogger<ArtifactDeploymentService>.Instance);
+    }
+
+    private static DeployArtifactsCommand CreateCommand()
+    {
+        return new DeployArtifactsCommand(
+            "dep1", null, null, null, null, DateTimeOffset.UtcNow);
+    }
+}