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_en.arb

@@ -1573,6 +1573,21 @@
   "doctorPathStudioErrors": "Studio errors",
   "settingsCategoryGeneral": "General",
   "settingsCategoryAppearance": "Appearance",
+  "settingsCategoryAbout": "About",
+  "aboutPanelTitle": "About Ch∆In",
+  "aboutPanelBody": "Product, vendor, and license details of this installation — every value is copyable.",
+  "aboutProduct": "Product",
+  "aboutStudioVersion": "Studio version",
+  "aboutHubVersion": "Hub version",
+  "aboutHubVersionUnknown": "not connected",
+  "aboutVendor": "Vendor",
+  "aboutAuthor": "Author",
+  "aboutLicense": "License",
+  "aboutContact": "Contact",
+  "aboutDocs": "Documentation",
+  "aboutOpenLink": "Open in browser",
+  "aboutCopyTooltip": "Copy",
+  "aboutCopiedToast": "Copied to the clipboard.",
   "sidebarSearchLabel": "Search & commands",
   "settingsSidebarPinnedTitle": "Keep the navigation expanded",
   "settingsSidebarPinnedBody": "Shows the sidebar labels permanently instead of only while hovering with the mouse.",