Add dummy LLM provider, update Concelier sources and JobEngine endpoints

- AdvisoryAI: DummyLlmProvider for offline/testing scenarios,
  wire in LlmProviderFactory
- Concelier: source definitions, registry, and management endpoint updates
- JobEngine: approval and release endpoint updates
- etc/llm-providers/dummy.yaml config

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

src/AdvisoryAI/StellaOps.AdvisoryAI/Inference/LlmProviders/DummyLlmProvider.cs

@@ -0,0 +1,80 @@
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using System.Runtime.CompilerServices;
+
+namespace StellaOps.AdvisoryAI.Inference.LlmProviders;
+
+/// <summary>
+/// Dummy LLM provider for testing. Reverses the user's question as the "answer"
+/// and streams it word by word to exercise the full SSE pipeline.
+/// </summary>
+public sealed class DummyLlmProvider : ILlmProvider
+{
+    public string ProviderId => "dummy";
+
+    public Task<bool> IsAvailableAsync(CancellationToken cancellationToken = default)
+        => Task.FromResult(true);
+
+    public Task<LlmCompletionResult> CompleteAsync(
+        LlmCompletionRequest request, CancellationToken cancellationToken = default)
+    {
+        var answer = BuildAnswer(request.UserPrompt);
+        return Task.FromResult(new LlmCompletionResult
+        {
+            Content = answer,
+            ModelId = "dummy-echo-reverse",
+            ProviderId = "dummy",
+            InputTokens = request.UserPrompt.Split(' ').Length,
+            OutputTokens = answer.Split(' ').Length,
+            FinishReason = "stop",
+            Deterministic = true,
+        });
+    }
+
+    public async IAsyncEnumerable<LlmStreamChunk> CompleteStreamAsync(
+        LlmCompletionRequest request,
+        [EnumeratorCancellation] CancellationToken cancellationToken = default)
+    {
+        var answer = BuildAnswer(request.UserPrompt);
+        var words = answer.Split(' ');
+
+        foreach (var word in words)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            await Task.Delay(60, cancellationToken); // simulate token-by-token streaming
+            yield return new LlmStreamChunk { Content = word + " ", IsFinal = false };
+        }
+
+        yield return new LlmStreamChunk { Content = "", IsFinal = true, FinishReason = "stop" };
+    }
+
+    public void Dispose() { }
+
+    private static string BuildAnswer(string userPrompt)
+    {
+        var reversed = new string(userPrompt.Reverse().ToArray());
+        return $"[Dummy echo-reverse provider] You asked: \"{userPrompt}\" — Reversed: \"{reversed}\"";
+    }
+}
+
+/// <summary>
+/// Plugin registration for the dummy provider.
+/// </summary>
+public sealed class DummyLlmProviderPlugin : ILlmProviderPlugin
+{
+    public string Name => "Dummy Echo-Reverse";
+    public string ProviderId => "dummy";
+    public string DisplayName => "Dummy Echo-Reverse";
+    public string Description => "Test provider that echoes and reverses the input. No external API needed.";
+    public string DefaultConfigFileName => "dummy.yaml";
+
+    public bool IsAvailable(IServiceProvider services) => true;
+
+    public LlmProviderConfigValidation ValidateConfiguration(IConfiguration configuration)
+        => LlmProviderConfigValidation.Success();
+
+    public ILlmProvider Create(IServiceProvider services, IConfiguration configuration)
+        => new DummyLlmProvider();
+}

src/AdvisoryAI/StellaOps.AdvisoryAI/Inference/LlmProviders/LlmProviderFactory.cs

@@ -135,6 +135,7 @@ public static class LlmProviderPluginExtensions
             catalog.RegisterPlugin(new GeminiLlmProviderPlugin());
             catalog.RegisterPlugin(new LlamaServerLlmProviderPlugin());
             catalog.RegisterPlugin(new OllamaLlmProviderPlugin());
+            catalog.RegisterPlugin(new DummyLlmProviderPlugin());
 
             // Load configurations from directory
             var fullPath = Path.GetFullPath(configDirectory);
@@ -170,6 +171,7 @@ public static class LlmProviderPluginExtensions
             catalog.RegisterPlugin(new GeminiLlmProviderPlugin());
             catalog.RegisterPlugin(new LlamaServerLlmProviderPlugin());
             catalog.RegisterPlugin(new OllamaLlmProviderPlugin());
+            catalog.RegisterPlugin(new DummyLlmProviderPlugin());
 
             configureCatalog(catalog);