feat: sample flows follow the hub's wire flag; examples group + import action

The Example chip used to come from a client-side content-marker
scan that had drifted from the hub's renamed sample header — no
current sample matched it. The host now passes the hub-reported
sample set (FlowSummary.sample) and the editor renders truth only:
no host info, no chips.

Samples collapse under one 'Examples (N)' group below the
operator's own flows (expanded only when nothing else exists), and
an optional onImportSamples action on the empty list is the
deliberate way to pull the bundled examples into a sealed area's
empty hub. Guard: flow_list_samples_test pins chips-from-host-only,
the grouping, and the import round trip.

Signed-off-by: flemming-it <sf@flemming.it>

lib/src/widgets.dart

@@ -12,11 +12,17 @@ class FaiEmptyState extends StatelessWidget {
   final IconData icon;
   final String title;
   final String? hint;
+
+  /// Optional action rendered under the hint (e.g. the empty flow
+  /// list's "import example flows" button).
+  final Widget? action;
+
   const FaiEmptyState({
     super.key,
     required this.icon,
     required this.title,
     this.hint,
+    this.action,
   });
 
   @override
@@ -46,6 +52,10 @@ class FaiEmptyState extends StatelessWidget {
                 textAlign: TextAlign.center,
               ),
             ],
+            if (action != null) ...[
+              const SizedBox(height: FaiSpace.md),
+              action!,
+            ],
           ],
         ),
       ),