feat(doctor): update banner via HubAdmin.CheckUpdate (v0.9.0)

Doctor page now opens with a slim banner above the summary strip
in two cases: an actually newer version on the channel ("Update
available — v0.x.y", success-tone "new" pill, release-notes URL
when present) or the release host being unreachable
("Release host unreachable", neutral "offline" pill, with the
network reason). When local matches latest the banner stays
hidden — quiet UI is the right default.

Hooks into the existing parallel-fetch in `HubService.doctor` so
the new RPC adds zero latency to the page load.

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

lib/data/hub.dart

@@ -210,12 +210,16 @@ class HubService {
             (_) => VerifyEventChainResponse(),
           ),
       _client.listServices().catchError((_) => <DeclaredService>[]),
+      _client.checkUpdate().catchError(
+            (_) => CheckUpdateResponse(),
+          ),
     ]);
 
     final caps = results[0] as List<CapabilityEntry>;
     final approvals = results[1] as List<PendingApprovalEntry>;
     final chain = results[2] as VerifyEventChainResponse;
     final services = results[3] as List<DeclaredService>;
+    final update = results[4] as CheckUpdateResponse;
 
     // Module count = distinct module_name across capabilities.
     final moduleNames = <String>{for (final c in caps) c.moduleName};
@@ -237,10 +241,40 @@ class HubService {
             ),
           )
           .toList(),
+      update: UpdateStatus(
+        channel: update.channel,
+        localVersion: update.localVersion,
+        latestVersion: update.latestVersion,
+        updateAvailable: update.updateAvailable,
+        manifestReachable: update.manifestReachable,
+        releaseNotesUrl:
+            update.releaseNotesUrl.isEmpty ? null : update.releaseNotesUrl,
+        reason: update.reason.isEmpty ? null : update.reason,
+      ),
     );
   }
 }
 
+class UpdateStatus {
+  final String channel;
+  final String localVersion;
+  final String latestVersion;
+  final bool updateAvailable;
+  final bool manifestReachable;
+  final String? releaseNotesUrl;
+  final String? reason;
+
+  const UpdateStatus({
+    required this.channel,
+    required this.localVersion,
+    required this.latestVersion,
+    required this.updateAvailable,
+    required this.manifestReachable,
+    this.releaseNotesUrl,
+    this.reason,
+  });
+}
+
 class DoctorSnapshot {
   final int moduleCount;
   final int capabilityCount;
@@ -249,6 +283,7 @@ class DoctorSnapshot {
   final int eventChainVerified;
   final String? eventChainTamperedAt;
   final List<ServiceEntry> services;
+  final UpdateStatus update;
 
   const DoctorSnapshot({
     required this.moduleCount,
@@ -258,6 +293,7 @@ class DoctorSnapshot {
     required this.eventChainVerified,
     required this.eventChainTamperedAt,
     required this.services,
+    required this.update,
   });
 
   bool get chainHealthy => eventChainTamperedAt == null;

lib/main.dart

@@ -22,7 +22,7 @@ import 'widgets/widgets.dart';
 /// Studio's own build version. Bump on every UI commit so the
 /// running app self-identifies — visible in the sidebar header
 /// and quick-glance proof that you're seeing the current build.
-const String kStudioVersion = '0.8.0';
+const String kStudioVersion = '0.9.0';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();

lib/pages/doctor.dart

@@ -59,9 +59,14 @@ class _DoctorPageState extends State<DoctorPage> {
             );
           }
           final s = snapshot.data!;
+          final showUpdate = s.update.updateAvailable ||
+              (!s.update.manifestReachable &&
+                  s.update.localVersion.isNotEmpty);
           return ListView(
             padding: const EdgeInsets.all(FaiSpace.xl),
             children: [
+              if (showUpdate) _UpdateBanner(status: s.update),
+              if (showUpdate) const SizedBox(height: FaiSpace.lg),
               _SummaryStrip(snapshot: s),
               const SizedBox(height: FaiSpace.xl),
               _Section(
@@ -431,3 +436,72 @@ class _ServicesPanel extends StatelessWidget {
     );
   }
 }
+
+class _UpdateBanner extends StatelessWidget {
+  final UpdateStatus status;
+
+  const _UpdateBanner({required this.status});
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final available = status.updateAvailable;
+    final iconData = available
+        ? Icons.system_update_alt_outlined
+        : Icons.cloud_off_outlined;
+    final iconColor = available
+        ? theme.colorScheme.primary
+        : theme.colorScheme.onSurfaceVariant;
+    final title = available
+        ? 'Update available — ${status.latestVersion}'
+        : 'Release host unreachable';
+    final body = available
+        ? 'Channel ${status.channel} now offers ${status.latestVersion}. '
+            'Apply with: fai update apply --channel ${status.channel}'
+        : (status.reason ?? 'Could not contact the release feed for ${status.channel}.');
+    return FaiCard(
+      child: Row(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Icon(iconData, size: 20, color: iconColor),
+          const SizedBox(width: FaiSpace.md),
+          Expanded(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(
+                  title,
+                  style: theme.textTheme.titleSmall?.copyWith(
+                    fontWeight: FontWeight.w600,
+                  ),
+                ),
+                const SizedBox(height: 2),
+                Text(
+                  body,
+                  style: FaiTheme.mono(
+                    size: 11,
+                    color: theme.colorScheme.onSurfaceVariant,
+                  ),
+                ),
+                if (available && status.releaseNotesUrl != null) ...[
+                  const SizedBox(height: 4),
+                  Text(
+                    'notes: ${status.releaseNotesUrl}',
+                    style: FaiTheme.mono(
+                      size: 11,
+                      color: theme.colorScheme.primary,
+                    ),
+                  ),
+                ],
+              ],
+            ),
+          ),
+          FaiPill(
+            label: available ? 'new' : 'offline',
+            tone: available ? FaiPillTone.success : FaiPillTone.neutral,
+          ),
+        ],
+      ),
+    );
+  }
+}