feat(settings): About section — vendor, versions, license, contact

Procurement personas found no vendor, version, license, or
support information anywhere in the app (a hard checklist fail
for regulated buyers). Settings gains an About category:
product name, Studio + running-hub version, vendor Flemming.AI,
author, Apache 2.0 license, contact address, and the docs URL —
every value selectable and one-click copyable. Studio version
constant moved to data/about_info.dart so sidebar tag and About
can never drift. Bumps Studio to 0.71.0.

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

lib/data/about_info.dart

@@ -0,0 +1,14 @@
+// Product identity shown in Settings → About and the sidebar
+// version tag. One place to bump so procurement-facing facts
+// (vendor, license, contact) can never drift between surfaces.
+
+/// Studio's own build version. Bump on every UI release so the
+/// running app self-identifies.
+const String kStudioVersion = '0.71.0';
+
+const String kProductName = 'Ch∆In Studio';
+const String kVendorName = 'Flemming.AI (F∆I)';
+const String kAuthorName = 'Dr. Stefan Flemming';
+const String kLicenseName = 'Apache 2.0';
+const String kContactEmail = 'chain@flemming.ai';
+const String kDocsUrl = 'https://chain.flemming.ai';

lib/data/hub.dart

@@ -1187,6 +1187,22 @@ class HubService {
   }
 
   /// Composite "doctor" snapshot. One round-trip per piece, run
+  /// Version string of the RUNNING hub (from CheckUpdate's
+  /// local_version — a local RPC field; the manifest fetch result
+  /// is ignored). Empty when the hub is unreachable. Used by
+  /// Settings → About.
+  Future<String> hubVersion() async {
+    try {
+      final r = await _client.checkUpdate().timeout(
+            const Duration(seconds: 2),
+            onTimeout: () => CheckUpdateResponse(),
+          );
+      return r.localVersion;
+    } catch (_) {
+      return '';
+    }
+  }
+
   /// in parallel so the page populates fast.
   Future<DoctorSnapshot> doctor() async {
     final results = await Future.wait([