Show next/previous blocks during recording

Summary

Add a display toggle that shows the next and previous blocks while recording so the performer stays oriented.

Recording mode can show previous and next script blocks around the active block.
The toggle helps orientation without obscuring recording controls or active text.
Add or update browser/UI test coverage for the relevant user flow.
Solution tests pass before the issue is marked ready for user verification.

Implemented in 442021f.

What changed:

Added a Go Live recording cue toggle in the top bar.
While recording, the program monitor can show compact previous/current/next script block context.
Added in-overlay next/previous cue controls so the active recording block can advance without covering the recording/streaming controls.
Added stable data-test selectors plus bUnit and Playwright coverage for the recording context flow.

Verification passed:

dotnet build ./PrompterOne.slnx -warnaserror --no-restore
dotnet test --project tests/PrompterOne.Web.Tests/PrompterOne.Web.Tests.csproj --no-build -- --no-ansi --no-progress (620/620)
dotnet test --project tests/PrompterOne.Web.UITests.Studio/PrompterOne.Web.UITests.Studio.csproj --no-build -- --no-ansi --no-progress (39/39)
dotnet test @./tests/dotnet-test-progress.rsp --solution ./PrompterOne.slnx (1171/1171)

Ready for review; leaving the issue open for human verification.