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.Scheduler.WebService.Tests/SchedulerPluginHostFactoryTests.cs

@@ -0,0 +1,73 @@
+using System;
+using System.IO;
+using StellaOps.Plugin.Hosting;
+using StellaOps.Scheduler.WebService.Hosting;
+using StellaOps.Scheduler.WebService.Options;
+using Xunit;
+
+namespace StellaOps.Scheduler.WebService.Tests;
+
+public class SchedulerPluginHostFactoryTests
+{
+    [Fact]
+    public void Build_usesDefaults_whenOptionsEmpty()
+    {
+        var options = new SchedulerOptions.PluginOptions();
+        var contentRoot = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(contentRoot);
+
+        try
+        {
+            var hostOptions = SchedulerPluginHostFactory.Build(options, contentRoot);
+
+            var expectedBase = Path.GetFullPath(Path.Combine(contentRoot, ".."));
+            var expectedPlugins = Path.Combine(expectedBase, "plugins", "scheduler");
+
+            Assert.Equal(expectedBase, hostOptions.BaseDirectory);
+            Assert.Equal(expectedPlugins, hostOptions.PluginsDirectory);
+            Assert.Single(hostOptions.SearchPatterns, "StellaOps.Scheduler.Plugin.*.dll");
+            Assert.True(hostOptions.EnsureDirectoryExists);
+            Assert.False(hostOptions.RecursiveSearch);
+            Assert.Empty(hostOptions.PluginOrder);
+        }
+        finally
+        {
+            Directory.Delete(contentRoot, recursive: true);
+        }
+    }
+
+    [Fact]
+    public void Build_respectsConfiguredValues()
+    {
+        var options = new SchedulerOptions.PluginOptions
+        {
+            BaseDirectory = Path.Combine(Path.GetTempPath(), "scheduler-options", Guid.NewGuid().ToString("N")),
+            Directory = Path.Combine("custom", "plugins"),
+            RecursiveSearch = true,
+            EnsureDirectoryExists = false
+        };
+
+        options.SearchPatterns.Add("Custom.Plugin.*.dll");
+        options.OrderedPlugins.Add("StellaOps.Scheduler.Plugin.Alpha");
+
+        Directory.CreateDirectory(options.BaseDirectory!);
+
+        try
+        {
+            var hostOptions = SchedulerPluginHostFactory.Build(options, contentRootPath: Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N")));
+
+            var expectedPlugins = Path.GetFullPath(Path.Combine(options.BaseDirectory!, options.Directory!));
+
+            Assert.Equal(options.BaseDirectory, hostOptions.BaseDirectory);
+            Assert.Equal(expectedPlugins, hostOptions.PluginsDirectory);
+            Assert.Single(hostOptions.SearchPatterns, "Custom.Plugin.*.dll");
+            Assert.Single(hostOptions.PluginOrder, "StellaOps.Scheduler.Plugin.Alpha");
+            Assert.True(hostOptions.RecursiveSearch);
+            Assert.False(hostOptions.EnsureDirectoryExists);
+        }
+        finally
+        {
+            Directory.Delete(options.BaseDirectory!, recursive: true);
+        }
+    }
+}