Allow media file attachments to blocks

[KSemenenko]

Summary

Allow users to attach media files and images directly to script blocks to provide essential context during the writing and performance phases.

Source

• Category: Script Editing
• Feedback video: https://youtu.be/IeUoMyx7dKE?t=46m2s

Acceptance criteria

• Users can attach media files and images to specific script blocks.
• Attachments are visible where they provide context during writing or performance.
• Attachment metadata persists locally without corrupting the script source.
• 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 ab5611b (Add block media attachments (#46)).

What changed:

• Added local per-script block attachment metadata storage, keyed by script block, without writing attachment metadata into TPS source.
• Added Cards view media attachment controls, image thumbnails/file chips, localized labels, and stable data-test selectors.
• Added teleprompter reader attachment context chips so attached media is visible during performance.
• Added browser UI coverage for attach -> source integrity -> editor reload persistence -> teleprompter visibility.

Verification:

• dotnet build ./PrompterOne.slnx -warnaserror --no-restore
• dotnet test --project tests/PrompterOne.Web.UITests.Editor/PrompterOne.Web.UITests.Editor.csproj --no-build -- --no-ansi --no-progress (154/154 passed)
• dotnet test --project tests/PrompterOne.Web.Tests/PrompterOne.Web.Tests.csproj -- --no-ansi --no-progress (598/598 passed)
• dotnet test @./tests/dotnet-test-progress.rsp --solution ./PrompterOne.slnx (1143/1143 passed)

Ready for review @byskyphy.