fix(runs): stop claiming the hub is unreachable on RPC-level errors

The runs monitor folded every load failure into 'hub not reachable',
contradicting the sidebar's green connected dot whenever the hub
answered but the RPC failed — most visibly against a pre-0.22 hub
whose version predates the ListInvocations RPC (UNIMPLEMENTED).

Classify the failure instead (top-level, unit-tested):
- UNIMPLEMENTED -> 'this view needs a newer hub version' with a
  doctor-page link (the update banner lives there)
- FAILED_PRECONDITION from the detached gate -> the regular
  feature-off empty state with the guide button
- UNAVAILABLE / DEADLINE_EXCEEDED / socket-level failures -> the
  honest 'hub not reachable' state (unchanged)
- everything else -> a load-failed state with the friendly error
  and a copyable detail box

The error view is a public callback-driven widget so the tests pump
each variant without a live hub. New DE+EN strings for the too-old
and load-failed states; grpcCodeOf/grpcMessageOf exposed from the
friendly-error mapper instead of duplicating the duck-typing.

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

lib/data/friendly_error.dart

@@ -217,6 +217,16 @@ FriendlyError? _matchHubPattern(String detail, AppLocalizations l) {
   return null;
 }
 
+/// Duck-typed `GrpcError.code` reader — public so pages that
+/// classify errors themselves (e.g. the runs monitor separating
+/// "hub down" from "hub too old") share one accessor instead of
+/// re-implementing the duck-typing.
+int? grpcCodeOf(Object error) => _intField(error, 'code');
+
+/// Duck-typed `GrpcError.message` reader — companion to
+/// [grpcCodeOf].
+String? grpcMessageOf(Object error) => _stringField(error, 'message');
+
 /// Try to read an `int` field by name off an arbitrary object.
 /// Returns `null` when the field doesn't exist or has another
 /// runtime type. Used to duck-type `GrpcError.code` without