Add clear in-app documentation

[KSemenenko]

Summary

Add a dedicated page or clear in-app explanations for how the standard and app work, so users don't have to seek out external tutorials.

Source

• Category: UI & Organization
• Feedback video: https://youtu.be/IeUoMyx7dKE?t=44m21s

Acceptance criteria

• PrompterOne includes clear in-app documentation or a dedicated help page for the app and TPS standard basics.
• Users can discover the help content from normal app navigation without external tutorials.
• The content is localized consistently with supported UI languages where user-facing text is added.
• Add or update browser/UI test coverage for the relevant user flow.
• Solution tests pass before the issue is marked ready for user verification.

[KSemenenko]

Implemented in b12cf9e and pushed to main.\n\nScope:\n- Added a discoverable Help section under Settings navigation.\n- Documented the PrompterOne workflow, TPS basics, writing/rehearsal modes, and local file/history behavior in-app.\n- Localized the added help text across the supported UI resource files.\n- Added Shell browser UI coverage for discovering and expanding the Help content.\n\nVerification:\n- dotnet build ./PrompterOne.slnx -warnaserror --no-restore\n- dotnet test --project tests/PrompterOne.Web.UITests.Shell/PrompterOne.Web.UITests.Shell.csproj --no-build -- --no-ansi --no-progress (60/60)\n- dotnet test @./tests/dotnet-test-progress.rsp --solution ./PrompterOne.slnx (1165/1165)\n\nReady for review @byskyphy.

[byskyphy]

this needs to be combined with the "tour" feature and elaborated.