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.

docs/ui/downloads.md

@@ -190,7 +190,7 @@ Telemetry entries include correlation IDs that match backend manifest refresh lo
 - `/docs/ui/sbom-explorer.md` - export flows feeding the downloads queue.  
 - `/docs/ui/runs.md` - evidence bundle integration.  
 - `/docs/24_OFFLINE_KIT.md` - offline kit packaging and verification.  
-- `/docs/security/console-security.md` - scopes, CSP, and download token handling (pending).  
+- `/docs/security/console-security.md` - scopes, CSP, and download token handling.  
 - `/docs/cli-vs-ui-parity.md` - CLI equivalence checks (pending).  
 - `deploy/releases/*.yaml` - source of container digests mirrored into the manifest.