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.Cartographer/TASKS.md

@@ -1,6 +1,6 @@
 # Cartographer Task Board — Epic 3: Graph Explorer v1
 | ID | Status | Owner(s) | Depends on | Description | Exit Criteria |
 |----|--------|----------|------------|-------------|---------------|
-| CARTO-GRAPH-21-010 | TODO | Cartographer Guild | AUTH-GRAPH-21-001 | Replace hard-coded `graph:*` scope strings in Cartographer services/clients with `StellaOpsScopes` constants; document new dependency. | All scope checks reference `StellaOpsScopes`; documentation updated; unit tests adjusted if needed. |
+| CARTO-GRAPH-21-010 | DONE (2025-10-27) | Cartographer Guild | AUTH-GRAPH-21-001 | Replace hard-coded `graph:*` scope strings in Cartographer services/clients with `StellaOpsScopes` constants; document new dependency. | All scope checks reference `StellaOpsScopes`; documentation updated; unit tests adjusted if needed. |
 
 > 2025-10-26 — Note: awaiting Cartographer service bootstrap. Keep this task open until Cartographer routes exist so we can swap to `StellaOpsScopes` immediately.