feat(studio): channel pill in sidebar + Featured strip in Store (v0.20.0)

Sidebar:
- New active-channel pill below the connection pill,
  color-coded so production deployments look visibly
  different from local-dev. Click opens Settings; tooltip
  explains the channel taxonomy. Polled in lockstep with the
  health probe so it tracks CLI-driven `fai channel switch`.

Store:
- Featured strip above the main grid renders editorial
  picks as bigger hero tiles with a subtle gradient
  backdrop, version + status pills, and a one-click
  Install. Hidden the moment the operator types in the
  search box or picks any filter — the result list is the
  answer they want, not editorial chrome.

StoreItem now carries the `featured` flag so the page can
filter without an extra round-trip.

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

lib/data/hub.dart

@@ -390,6 +390,7 @@ class HubService {
             bestVersion: e.bestVersion,
             status: e.status,
             installed: e.installed,
+            featured: e.featured,
           ),
         )
         .toList();
@@ -1060,6 +1061,10 @@ class StoreItem {
   /// "published", "alpha", "planned", or empty when unknown.
   final String status;
   final bool installed;
+  /// True iff the store-index marks this entry as editorially
+  /// featured (curated quarterly in the bundled seed.yaml).
+  /// Drives the "Featured" strip at the top of the Store page.
+  final bool featured;
 
   const StoreItem({
     required this.name,
@@ -1076,5 +1081,6 @@ class StoreItem {
     required this.bestVersion,
     required this.status,
     required this.installed,
+    required this.featured,
   });
 }