Add StellaOps.Workflow engine: 14 libraries, WebService, 8 test projects

Extract product-agnostic workflow engine from Ablera.Serdica.Workflow into
standalone StellaOps.Workflow.* libraries targeting net10.0.

Libraries (14):
- Contracts, Abstractions (compiler, decompiler, expression runtime)
- Engine (execution, signaling, scheduling, projections, hosted services)
- ElkSharp (generic graph layout algorithm)
- Renderer.ElkSharp, Renderer.ElkJs, Renderer.Msagl, Renderer.Svg
- Signaling.Redis, Signaling.OracleAq
- DataStore.MongoDB, DataStore.PostgreSQL, DataStore.Oracle

WebService: ASP.NET Core Minimal API with 22 endpoints

Tests (8 projects, 109 tests pass):
- Engine.Tests (105 pass), WebService.Tests (4 E2E pass)
- Renderer.Tests, DataStore.MongoDB/Oracle/PostgreSQL.Tests
- Signaling.Redis.Tests, IntegrationTests.Shared

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/workflow/tutorials/04-human-tasks/csharp/ApprovalWorkflow.cs

@@ -0,0 +1,101 @@
+using System.Collections.Generic;
+using System.Text.Json;
+
+using WorkflowEngine.Abstractions;
+using WorkflowEngine.Contracts;
+
+namespace WorkflowEngine.Tutorials;
+
+public sealed class ApprovalRequest
+{
+    public long PolicyId { get; set; }
+    public long AnnexId { get; set; }
+}
+
+public sealed class ApprovalWorkflow : IDeclarativeWorkflow<ApprovalRequest>
+{
+    public string WorkflowName => "ApprovalExample";
+    public string WorkflowVersion => "1.0.0";
+    public string DisplayName => "Approval Example";
+    public IReadOnlyCollection<string> WorkflowRoles => ["DBA", "UR_UNDERWRITER"];
+
+    public WorkflowSpec<ApprovalRequest> Spec { get; } = WorkflowSpec
+        .For<ApprovalRequest>()
+        .InitializeState(WorkflowExpr.Object(
+            WorkflowExpr.Prop("policyId", WorkflowExpr.Path("start.policyId")),
+            WorkflowExpr.Prop("annexId", WorkflowExpr.Path("start.annexId"))))
+
+        // Register the task definition (separate from activation).
+        .AddTask(approveTask)
+
+        // Start flow: validate, then activate the approval task.
+        .StartWith(flow => flow
+            .Call("Validate",
+                Address.LegacyRabbit("pas_policy_validate"),
+                WorkflowExpr.Object(
+                    WorkflowExpr.Prop("policyId", WorkflowExpr.Path("state.policyId"))),
+                WorkflowHandledBranchAction.Complete,
+                WorkflowHandledBranchAction.Complete)
+            .ActivateTask("Approve Policy"))                  // pauses here
+        .Build();
+
+    public IReadOnlyCollection<WorkflowTaskDescriptor> Tasks => Spec.TaskDescriptors;
+
+    // Define the human task with roles, payload, optional deadline, and OnComplete flow.
+    private static readonly WorkflowHumanTaskDefinition<ApprovalRequest> approveTask =
+        WorkflowHumanTask.For<ApprovalRequest>(
+                "Approve Policy",                              // task name
+                "PolicyApproval",                              // task type (UI component)
+                "business/policies",                           // route
+                taskRoles: ["UR_UNDERWRITER"])                 // only underwriters
+            .WithPayload(WorkflowExpr.Object(
+                WorkflowExpr.Prop("policyId", WorkflowExpr.Path("state.policyId")),
+                WorkflowExpr.Prop("annexId", WorkflowExpr.Path("state.annexId"))))
+            .WithTimeout(86400)                                // 24-hour deadline (optional)
+            .OnComplete(BuildApprovalFlow);
+
+    private static void BuildApprovalFlow(WorkflowFlowBuilder<ApprovalRequest> flow)
+    {
+        flow
+            // Store the user's answer in state for auditability.
+            .Set("answer", WorkflowExpr.Path("payload.answer"))
+
+            // Branch on the answer.
+            .WhenPayloadEquals("answer", "reject", "Rejected?",
+                rejected => rejected
+                    .Call("Cancel Application",
+                        Address.LegacyRabbit("pas_annexprocessing_cancelaplorqt"),
+                        WorkflowExpr.Object(
+                            WorkflowExpr.Prop("policyId", WorkflowExpr.Path("state.policyId"))),
+                        WorkflowHandledBranchAction.Complete,
+                        WorkflowHandledBranchAction.Complete)
+                    .Complete(),
+
+                approved => approved
+                    .Call<object>("Perform Operations",
+                        Address.LegacyRabbit("pas_operations_perform",
+                            SerdicaLegacyRabbitMode.MicroserviceConsumer),
+                        WorkflowExpr.Object(
+                            WorkflowExpr.Prop("policyId", WorkflowExpr.Path("state.policyId")),
+                            WorkflowExpr.Prop("stages", WorkflowExpr.Array(
+                                WorkflowExpr.String("UNDERWRITING"),
+                                WorkflowExpr.String("CONFIRMATION")))),
+                        WorkflowHandledBranchAction.Complete,
+                        WorkflowHandledBranchAction.Complete,
+                        resultKey: "operations")
+                    .Set("passed", WorkflowExpr.Path("result.operations.passed"))
+
+                    .WhenStateFlag("passed", true, "Operations Passed?",
+                        passed => passed
+                            .Call("Convert To Policy",
+                                Address.LegacyRabbit("pas_polreg_convertapltopol"),
+                                WorkflowExpr.Object(
+                                    WorkflowExpr.Prop("policyId", WorkflowExpr.Path("state.policyId"))),
+                                WorkflowHandledBranchAction.Complete,
+                                WorkflowHandledBranchAction.Complete)
+                            .Complete(),
+
+                        // Operations failed: re-open the same task for the user to fix and retry.
+                        failed => failed.ActivateTask("Approve Policy")));
+    }
+}