Add toggle to disable auto-loop

Summary

Add a toggle to turn off the auto-loop feature, preventing the app from automatically jumping back to the beginning of the script.

Users can disable automatic looping in reader/playback workflows.
When disabled, reaching the end of the script does not jump back to the beginning automatically.
The setting persists where the app already persists reader preferences.
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 caa51cc.

What changed:

Added a persisted teleprompter reader Auto-loop preference, defaulting to the existing looping behavior.
Added a reader transport toggle with aria/data-test coverage.
When Auto-loop is off, playback stops at the final word instead of wrapping back to the first block.
Added legacy ReaderSettings serialization coverage plus component and browser UI tests for persistence and stop-at-end behavior.

Verification passed:

dotnet build ./PrompterOne.slnx -warnaserror --no-restore
dotnet test --project tests/PrompterOne.Core.Tests/PrompterOne.Core.Tests.csproj --no-build -- --no-ansi --no-progress (125/125)
dotnet test --project tests/PrompterOne.Web.Tests/PrompterOne.Web.Tests.csproj --no-build -- --no-ansi --no-progress (619/619)
dotnet test --project tests/PrompterOne.Web.UITests.Reader/PrompterOne.Web.UITests.Reader.csproj --no-build -- --no-ansi --no-progress (170/170)
dotnet test @./tests/dotnet-test-progress.rsp --solution ./PrompterOne.slnx (1169/1169)

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