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/l10n/app_de.arb

@@ -1773,6 +1773,10 @@
   "runsEmptyHint": "Hier erscheinen Läufe, die im Hintergrund weiterlaufen, während Sie anderes tun. Diese Funktion ist optional und standardmäßig ausgeschaltet — die Anleitung zeigt Schritt für Schritt, wie sie eingeschaltet wird.",
   "runsEmptyEnabledHint": "Läufe im Hintergrund sind eingeschaltet — es wurde nur noch keiner gestartet. Starten Sie einen Flow mit der Option „im Hintergrund ausführen“, dann erscheint er hier.",
   "runsEmptyGuideButton": "Anleitung öffnen",
+  "runsHubTooOldTitle": "Diese Ansicht braucht eine neuere Hub-Version",
+  "runsHubTooOldHint": "Der Hub ist verbunden, aber seine Version kennt die Laufübersicht noch nicht. Aktualisieren Sie den Hub, dann erscheinen die Läufe hier.",
+  "runsHubTooOldButton": "Diagnose öffnen",
+  "runsLoadFailedTitle": "Läufe konnten nicht geladen werden",
   "runsCancelButton": "Abbrechen",
   "runsCancelSignalled": "Abbruch für {flow} ausgelöst.",
   "@runsCancelSignalled": {"placeholders": {"flow": {"type": "String"}}},

lib/l10n/app_en.arb

@@ -1812,6 +1812,10 @@
   "runsEmptyHint": "Runs that keep working in the background while you do something else appear here. The feature is optional and off by default — the guide shows step by step how to turn it on.",
   "runsEmptyEnabledHint": "Background runs are switched on — none has been started yet. Start a flow with the \"run in background\" option and it will appear here.",
   "runsEmptyGuideButton": "Open the guide",
+  "runsHubTooOldTitle": "This view needs a newer hub version",
+  "runsHubTooOldHint": "The hub is connected, but its version does not know the runs monitor yet. Update the hub and the runs will appear here.",
+  "runsHubTooOldButton": "Open Doctor",
+  "runsLoadFailedTitle": "Runs could not be loaded",
   "runsCancelButton": "Cancel",
   "runsCancelSignalled": "Cancel signalled for {flow}.",
   "@runsCancelSignalled": {"placeholders": {"flow": {"type": "String"}}},

lib/l10n/app_localizations.dart

@@ -5401,6 +5401,30 @@ abstract class AppLocalizations {
   /// **'Open the guide'**
   String get runsEmptyGuideButton;
 
+  /// No description provided for @runsHubTooOldTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'This view needs a newer hub version'**
+  String get runsHubTooOldTitle;
+
+  /// No description provided for @runsHubTooOldHint.
+  ///
+  /// In en, this message translates to:
+  /// **'The hub is connected, but its version does not know the runs monitor yet. Update the hub and the runs will appear here.'**
+  String get runsHubTooOldHint;
+
+  /// No description provided for @runsHubTooOldButton.
+  ///
+  /// In en, this message translates to:
+  /// **'Open Doctor'**
+  String get runsHubTooOldButton;
+
+  /// No description provided for @runsLoadFailedTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Runs could not be loaded'**
+  String get runsLoadFailedTitle;
+
   /// No description provided for @runsCancelButton.
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_de.dart

@@ -3198,6 +3198,20 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get runsEmptyGuideButton => 'Anleitung öffnen';
 
+  @override
+  String get runsHubTooOldTitle =>
+      'Diese Ansicht braucht eine neuere Hub-Version';
+
+  @override
+  String get runsHubTooOldHint =>
+      'Der Hub ist verbunden, aber seine Version kennt die Laufübersicht noch nicht. Aktualisieren Sie den Hub, dann erscheinen die Läufe hier.';
+
+  @override
+  String get runsHubTooOldButton => 'Diagnose öffnen';
+
+  @override
+  String get runsLoadFailedTitle => 'Läufe konnten nicht geladen werden';
+
   @override
   String get runsCancelButton => 'Abbrechen';
 

lib/l10n/app_localizations_en.dart

@@ -3195,6 +3195,19 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get runsEmptyGuideButton => 'Open the guide';
 
+  @override
+  String get runsHubTooOldTitle => 'This view needs a newer hub version';
+
+  @override
+  String get runsHubTooOldHint =>
+      'The hub is connected, but its version does not know the runs monitor yet. Update the hub and the runs will appear here.';
+
+  @override
+  String get runsHubTooOldButton => 'Open Doctor';
+
+  @override
+  String get runsLoadFailedTitle => 'Runs could not be loaded';
+
   @override
   String get runsCancelButton => 'Cancel';