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-stats.json

@@ -0,0 +1,24 @@
+{
+  "totalEntries": 4,
+  "pendingEntries": 2,
+  "replayingEntries": 0,
+  "replayedEntries": 1,
+  "resolvedEntries": 1,
+  "exhaustedEntries": 0,
+  "expiredEntries": 0,
+  "retryableEntries": 3,
+  "byCategory": {
+    "quota_exceeded": 2,
+    "upstream_error": 2
+  },
+  "topErrorCodes": {
+    "invalid_payload": 1,
+    "quota_exceeded": 2,
+    "upstream_timeout": 1
+  },
+  "topJobTypes": {
+    "export": 2,
+    "pack-run": 2
+  },
+  "traceId": "trace-sample"
+}