feat: add Reachability Center and Why Drawer components with tests

- Implemented ReachabilityCenterComponent for displaying asset reachability status with summary and filtering options.
- Added ReachabilityWhyDrawerComponent to show detailed reachability evidence and call paths.
- Created unit tests for both components to ensure functionality and correctness.
- Updated accessibility test results for the new components.

docs/api/gateway/samples/vex-statements-list.json

@@ -0,0 +1,18 @@
+{
+  "items": [
+    {
+      "statementId": "vex::tenant-default::CVE-2024-12345::001",
+      "vulnId": "CVE-2024-12345",
+      "productId": "asset::registry.local/ops/auth",
+      "status": "not_affected",
+      "justification": "Component not present in runtime image.",
+      "updatedAt": "2025-12-10T00:00:00Z",
+      "etag": "\"vex-001-v1\""
+    }
+  ],
+  "count": 1,
+  "continuationToken": null,
+  "etag": "\"vex-statements-sample-v1\"",
+  "traceId": "trace-sample-2"
+}
+