feat(learn): add web-only indicator icon and direct browser launch fo…

[rohanesor]

Description

Adds a visual indicator (open_in_new icon) to course cards on the Learn page for superblocks that require a web browser (Coding Interview Prep, Project Euler, Rosetta Code, The Odin Project, Foundational C# with Microsoft). Tapping these cards now routes the user directly to the course in the web browser instead of showing a snackbar message or opening incomplete in-app templates.

Motivation & Context

Previously, web-only courses looked identical to mobile-native courses with an arrow (>) icon. Users only discovered that a course required a web browser after tapping it, resulting in an inconsistent user experience.

Changes Made

• mobile-app/lib/ui/views/learn/utils/learn_globals.dart: Added webOnlySuperBlocks registry listing dashed names of browser-required courses (following existing hasNoCert, hasDialogue, and chapterBasedSuperBlocks patterns).
• mobile-app/lib/ui/views/learn/landing/landing_viewmodel.dart: Added openInBrowser(String dashedName) to launch ${AuthenticationService.baseURL}/learn/$dashedName using url_launcher.
• mobile-app/lib/ui/views/learn/landing/landing_view.dart:
  • Displays Icons.open_in_new trailing icon for web-only courses.
  • Adds Tooltip showing "Not available use the web version" (context.t.not_available_web) on long press.
  • Directly launches browser on tap when isWebOnly is true.

Checklist

• Tested and verified no regressions on mobile-native courses.
• Follows existing project architecture and naming conventions.
• Reuses existing localization keys (not_available_web).
• Clean minimal changes (~35 lines across 3 files).