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_de.arb

@@ -1549,6 +1549,21 @@
   "doctorPathStudioErrors": "Studio-Fehler",
   "settingsCategoryGeneral": "Allgemein",
   "settingsCategoryAppearance": "Darstellung",
+  "settingsCategoryAbout": "Über",
+  "aboutPanelTitle": "Über Ch∆In",
+  "aboutPanelBody": "Produkt-, Hersteller- und Lizenzangaben dieser Installation — alle Werte sind kopierbar.",
+  "aboutProduct": "Produkt",
+  "aboutStudioVersion": "Studio-Version",
+  "aboutHubVersion": "Hub-Version",
+  "aboutHubVersionUnknown": "nicht verbunden",
+  "aboutVendor": "Hersteller",
+  "aboutAuthor": "Autor",
+  "aboutLicense": "Lizenz",
+  "aboutContact": "Kontakt",
+  "aboutDocs": "Dokumentation",
+  "aboutOpenLink": "Im Browser öffnen",
+  "aboutCopyTooltip": "Kopieren",
+  "aboutCopiedToast": "In die Zwischenablage kopiert.",
   "sidebarSearchLabel": "Suchen & Befehle",
   "settingsSidebarPinnedTitle": "Navigation immer ausgeklappt",
   "settingsSidebarPinnedBody": "Zeigt die Beschriftungen der Seitenleiste dauerhaft an, statt sie nur beim Überfahren mit der Maus einzublenden.",