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/l10n/app_localizations_en.dart

@@ -2668,6 +2668,52 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get settingsCategoryAppearance => 'Appearance';
 
+  @override
+  String get settingsCategoryAbout => 'About';
+
+  @override
+  String get aboutPanelTitle => 'About Ch∆In';
+
+  @override
+  String get aboutPanelBody =>
+      'Product, vendor, and license details of this installation — every value is copyable.';
+
+  @override
+  String get aboutProduct => 'Product';
+
+  @override
+  String get aboutStudioVersion => 'Studio version';
+
+  @override
+  String get aboutHubVersion => 'Hub version';
+
+  @override
+  String get aboutHubVersionUnknown => 'not connected';
+
+  @override
+  String get aboutVendor => 'Vendor';
+
+  @override
+  String get aboutAuthor => 'Author';
+
+  @override
+  String get aboutLicense => 'License';
+
+  @override
+  String get aboutContact => 'Contact';
+
+  @override
+  String get aboutDocs => 'Documentation';
+
+  @override
+  String get aboutOpenLink => 'Open in browser';
+
+  @override
+  String get aboutCopyTooltip => 'Copy';
+
+  @override
+  String get aboutCopiedToast => 'Copied to the clipboard.';
+
   @override
   String get sidebarSearchLabel => 'Search & commands';