feat: Add VEX Status Chip component and integration tests for reachability drift detection

- Introduced `VexStatusChipComponent` to display VEX status with color coding and tooltips.
- Implemented integration tests for reachability drift detection, covering various scenarios including drift detection, determinism, and error handling.
- Enhanced `ScannerToSignalsReachabilityTests` with a null implementation of `ICallGraphSyncService` for better test isolation.
- Updated project references to include the new Reachability Drift library.

src/Scanner/StellaOps.Scanner.WebService/Security/ScannerPolicies.cs

@@ -5,6 +5,7 @@ internal static class ScannerPolicies
     public const string ScansEnqueue = "scanner.api";
     public const string ScansRead = "scanner.scans.read";
     public const string ScansWrite = "scanner.scans.write";
+    public const string ScansApprove = "scanner.scans.approve";
     public const string Reports = "scanner.reports";
     public const string RuntimeIngest = "scanner.runtime.ingest";
     public const string CallGraphIngest = "scanner.callgraph.ingest";