feat(deployment-manager): resolve DeploymentManager-006 — query site deployment state before redeploy and reconcile

Adds DeploymentStateQuery request/response contracts (Commons), a site-side
handler (SiteRuntime), a CommunicationService query method (Communication), and
reconciliation in DeploymentService: when a prior record is InProgress or
Failed-on-timeout, query the site; if it already holds the target revision hash
mark the record Success without re-sending; on query failure fall through to a
normal deploy (site-side stale-rejection is the safety net).

src/ScadaLink.Commons/Messages/Deployment/DeploymentStateQueryRequest.cs

@@ -0,0 +1,13 @@
+namespace ScadaLink.Commons.Messages.Deployment;
+
+/// <summary>
+/// Central→site query for the currently-applied deployment state of a single
+/// instance. Issued by the Deployment Manager before a re-deploy when a prior
+/// deployment record is stuck <c>InProgress</c> or <c>Failed</c> due to a
+/// timeout, so the site's actual state can be reconciled against the target
+/// revision before re-sending a deployment ("Deployment Identity &amp; Idempotency").
+/// </summary>
+public record DeploymentStateQueryRequest(
+    string CorrelationId,
+    string InstanceUniqueName,
+    DateTimeOffset Timestamp);

src/ScadaLink.Commons/Messages/Deployment/DeploymentStateQueryResponse.cs

@@ -0,0 +1,15 @@
+namespace ScadaLink.Commons.Messages.Deployment;
+
+/// <summary>
+/// Site→central response carrying the instance's currently-applied deployment
+/// state. If <see cref="IsDeployed"/> is <c>false</c> the instance has no
+/// deployed configuration at the site and <see cref="AppliedDeploymentId"/> /
+/// <see cref="AppliedRevisionHash"/> are <c>null</c>.
+/// </summary>
+public record DeploymentStateQueryResponse(
+    string CorrelationId,
+    string InstanceUniqueName,
+    bool IsDeployed,
+    string? AppliedDeploymentId,
+    string? AppliedRevisionHash,
+    DateTimeOffset Timestamp);