feat(test): hermetic hub fake + state-matrix sweep across all pages

The widget suites used to talk to whatever listens on the real
endpoint — results depended on the operator's machine (a running
hub fed real data into a11y/responsive runs and its gRPC channel
timers caused the historic flake). Hardening round:

- HubService.instance is now injectable (debugSetInstance);
  FakeHubService (test/support/fake_hub.dart) answers every member
  the pages touch with healthy-empty defaults and scripts per-RPC
  failures (UNIMPLEMENTED / UNAVAILABLE / detached gate) through a
  GrpcError-shaped fake. Unimplemented members are recorded and
  fail the sweep with the exact list.
- state_matrix_test.dart pins the app-wide invariants for every
  sidebar page x hub condition: healthy => no unreachable claims
  and no raw error text; hub gone => honest unreachable states;
  UNIMPLEMENTED => never 'not reachable' while the sidebar shows
  connected; detached gate => plain-language feature-off state.
- a11y + responsive sweeps now inject the fake (hermetic); the
  6-minute idle-timer drain workaround is gone with the cause.

Real bugs the new sweep caught immediately:
- every data page (store, doctor, audit, approvals, federation)
  folded ANY load failure into 'hub not reachable' — the runs-page
  bug class; they now share HubLoadErrorView, which classifies
  into unreachable / needs-newer-hub / load-failed-with-copyable-
  detail (new generic DE+EN strings)
- the approvals page's hidden tab had no future listener: a load
  failure there surfaced as an uncaught async error
- the audit status bar rendered the raw gRPC error wall verbatim;
  it now shows the classified friendly headline (still selectable)

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/pages/runs.dart

@@ -51,30 +51,22 @@ enum RunsLoadIssue {
 }
 
 /// Classify a [HubService.listDetachedRuns] failure into the view
-/// state the page should render.
+/// state the page should render. The runs-specific part is the
+/// detached feature gate; everything else delegates to the shared
+/// page-load classification.
 RunsLoadIssue classifyRunsLoadError(Object error) {
-  switch (grpcCodeOf(error)) {
-    case 12: // UNIMPLEMENTED — hub predates the RPC
-      return RunsLoadIssue.unsupported;
-    case 9: // FAILED_PRECONDITION — the hub's detached gate
-      final msg = (grpcMessageOf(error) ?? '').toLowerCase();
-      return msg.contains('detached')
-          ? RunsLoadIssue.featureDisabled
-          : RunsLoadIssue.other;
-    case 4: // DEADLINE_EXCEEDED
-    case 14: // UNAVAILABLE
-      return RunsLoadIssue.unreachable;
+  if (grpcCodeOf(error) == 9) {
+    // FAILED_PRECONDITION — the hub's detached gate.
+    final msg = (grpcMessageOf(error) ?? '').toLowerCase();
+    return msg.contains('detached')
+        ? RunsLoadIssue.featureDisabled
+        : RunsLoadIssue.other;
   }
-  // Non-gRPC failures: only clear socket-level shapes count as
-  // "unreachable"; everything else keeps its real story.
-  final s = error.toString().toLowerCase();
-  if (s.contains('socketexception') ||
-      s.contains('connection refused') ||
-      s.contains('connection terminated') ||
-      s.contains('failed to connect')) {
-    return RunsLoadIssue.unreachable;
-  }
-  return RunsLoadIssue.other;
+  return switch (classifyHubLoadError(error)) {
+    HubLoadIssue.unreachable => RunsLoadIssue.unreachable,
+    HubLoadIssue.unsupported => RunsLoadIssue.unsupported,
+    HubLoadIssue.other => RunsLoadIssue.other,
+  };
 }
 
 /// The error rendition of the runs monitor — public + callback-driven