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.Cli/appsettings.json

@@ -1,8 +1,9 @@
 {
   "StellaOps": {
-    "ApiKey": "",
-    "BackendUrl": "",
-    "ScannerCacheDirectory": "scanners",
+    "ApiKey": "",
+    "BackendUrl": "",
+    "ConcelierUrl": "",
+    "ScannerCacheDirectory": "scanners",
     "ResultsDirectory": "results",
     "DefaultRunner": "dotnet",
     "ScannerSignaturePublicKeyPath": "",