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/policy-exceptions.md

@@ -0,0 +1,26 @@
+# Policy + Exceptions Gateway Contract (draft v0.1)
+
+Scope: expose policy evaluation results that include exception metadata, plus simulation endpoints that accept exception overrides for what-if analysis.
+
+## Security / headers
+- `Authorization: Bearer <token>` (or `DPoP` where configured)
+- `X-StellaOps-Tenant: <tenantId>` (required)
+- `X-Stella-Project: <projectId>` (optional)
+- `X-Stella-Trace-Id: <traceId>` (optional; clients SHOULD send one)
+- Scopes:
+  - `POST /policy/effective`: `policy:read` AND `exception:read`
+  - `POST /policy/simulate`: `policy:simulate` AND `exception:read`
+
+## Endpoints
+- `POST /policy/effective` — deterministic effective policy view over a list of findings.
+- `POST /policy/simulate` — simulate policy result changes with exception overrides.
+
+## Request/response notes
+- Requests MUST remain deterministic: stable ordering, ISO-8601 UTC timestamps only.
+- Pagination uses `limit` (max `200`) and `continuationToken` (opaque string).
+- Exception metadata SHOULD reuse the Exception schema (`docs/api/console/exception-schema.md`) but MAY omit large fields like audit trails.
+
+## Samples
+- `docs/api/gateway/samples/policy-effective-sample.json`
+- `docs/api/gateway/samples/policy-simulate-sample.json`
+