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/orchestrator-deadletter-summary.json

@@ -0,0 +1,21 @@
+{
+  "items": [
+    {
+      "errorCode": "quota_exceeded",
+      "category": "quota_exceeded",
+      "entryCount": 2,
+      "retryableCount": 2,
+      "oldestEntry": "2025-12-10T00:00:00Z",
+      "sampleReason": "Quota exceeded for job type export."
+    },
+    {
+      "errorCode": "upstream_timeout",
+      "category": "upstream_error",
+      "entryCount": 1,
+      "retryableCount": 1,
+      "oldestEntry": "2025-12-11T00:00:00Z",
+      "sampleReason": "Upstream service timeout."
+    }
+  ],
+  "traceId": "trace-sample"
+}