Add toggle to disable auto-loop

[KSemenenko]

Summary

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

Source

• Category: Teleprompter & Prep
• Feedback video: https://youtu.be/IeUoMyx7dKE?t=41m28s

Acceptance criteria

• 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.

[KSemenenko]

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.