Form preview: option-source links, header, and View/Preview links

[maebeale]

🔗 Stacked PR — the base (maebeale/subtitle-field, #1635) is now merged into main; this PR has been rebased onto main. Third PR in the stack (builder UI) follows.

What is the goal of this PR and why is this important?

• The form preview gave little context, and dynamic-option fields gave no hint about where their choices come from. This makes the preview read as clear admin chrome and links dynamic fields to the lists that manage them.

How did you approach the change?

• Option-source links: dynamic-option fields (sourced from Sectors/Categories) show an "Options from …" link to their managed list — beside the visibility badge, or the field label when there's no badge.
• Preview header: now shows the form name, role, and an amber "Preview" badge signaling it's not the live page.
• Editor links: always offer a standalone "Preview"; add "View" to the live registration form when the originating event is known.

UI Testing Checklist

• Preview header shows form name, role, and the amber "Preview" badge.
• A dynamic-option field shows an "Options from …" link to the managed list on the preview.
• Editor shows "Preview" with no event; "View" + "Preview" when an event is known (View → live registration page).

Anything else to add?

• Second of three stacked PRs (subtitle → preview → builder UI).
• Rebased onto main after Make field subtitles editable in the form editor #1635 merged; updated the request spec for the renamed single_select_radio answer type (was multiple_choice_radio, renamed in Render dynamic-option fields as single-choice radio; align workshop settings #1634).