feat: Implement Scheduler Worker Options and Planner Loop

- Added `SchedulerWorkerOptions` class to encapsulate configuration for the scheduler worker.
- Introduced `PlannerBackgroundService` to manage the planner loop, fetching and processing planning runs.
- Created `PlannerExecutionService` to handle the execution logic for planning runs, including impact targeting and run persistence.
- Developed `PlannerExecutionResult` and `PlannerExecutionStatus` to standardize execution outcomes.
- Implemented validation logic within `SchedulerWorkerOptions` to ensure proper configuration.
- Added documentation for the planner loop and impact targeting features.
- Established health check endpoints and authentication mechanisms for the Signals service.
- Created unit tests for the Signals API to ensure proper functionality and response handling.
- Configured options for authority integration and fallback authentication methods.

src/StellaOps.Signals.Tests/SignalsApiTests.cs

@@ -0,0 +1,70 @@
+using System.Net;
+using System.Net.Http.Json;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Xunit;
+
+namespace StellaOps.Signals.Tests;
+
+public class SignalsApiTests : IClassFixture<WebApplicationFactory<Program>>
+{
+    private readonly WebApplicationFactory<Program> factory;
+
+    public SignalsApiTests(WebApplicationFactory<Program> factory)
+    {
+        this.factory = factory;
+    }
+
+    [Fact]
+    public async Task Healthz_ReturnsOk()
+    {
+        var client = factory.CreateClient();
+        var response = await client.GetAsync("/healthz");
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task Readyz_ReturnsOk()
+    {
+        var client = factory.CreateClient();
+        var response = await client.GetAsync("/readyz");
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        var payload = await response.Content.ReadFromJsonAsync<Dictionary<string, string>>();
+        Assert.NotNull(payload);
+        Assert.Equal("ready", payload!["status"]);
+    }
+
+    [Fact]
+    public async Task Ping_WithoutScopeHeader_ReturnsUnauthorized()
+    {
+        var client = factory.CreateClient();
+        var response = await client.GetAsync("/signals/ping");
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task Ping_WithMissingScope_ReturnsForbidden()
+    {
+        var client = factory.CreateClient();
+        var request = new HttpRequestMessage(HttpMethod.Get, "/signals/ping");
+        request.Headers.Add("X-Scopes", "signals:write");
+
+        var response = await client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task Ping_WithReadScope_ReturnsNoContent()
+    {
+        var client = factory.CreateClient();
+        var request = new HttpRequestMessage(HttpMethod.Get, "/signals/ping");
+        request.Headers.Add("X-Scopes", "signals:read");
+
+        var response = await client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
+    }
+}