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_de.dart

@@ -2666,6 +2666,52 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get settingsCategoryAppearance => 'Darstellung';
 
+  @override
+  String get settingsCategoryAbout => 'Über';
+
+  @override
+  String get aboutPanelTitle => 'Über Ch∆In';
+
+  @override
+  String get aboutPanelBody =>
+      'Produkt-, Hersteller- und Lizenzangaben dieser Installation — alle Werte sind kopierbar.';
+
+  @override
+  String get aboutProduct => 'Produkt';
+
+  @override
+  String get aboutStudioVersion => 'Studio-Version';
+
+  @override
+  String get aboutHubVersion => 'Hub-Version';
+
+  @override
+  String get aboutHubVersionUnknown => 'nicht verbunden';
+
+  @override
+  String get aboutVendor => 'Hersteller';
+
+  @override
+  String get aboutAuthor => 'Autor';
+
+  @override
+  String get aboutLicense => 'Lizenz';
+
+  @override
+  String get aboutContact => 'Kontakt';
+
+  @override
+  String get aboutDocs => 'Dokumentation';
+
+  @override
+  String get aboutOpenLink => 'Im Browser öffnen';
+
+  @override
+  String get aboutCopyTooltip => 'Kopieren';
+
+  @override
+  String get aboutCopiedToast => 'In die Zwischenablage kopiert.';
+
   @override
   String get sidebarSearchLabel => 'Suchen & Befehle';