page-status: BYOM content always shows 'No source'

[shsteimer]

For BYOM (Bring Your Own Markup) pages the sourceLastModified field from the admin API is null/absent. This causes classifySequenceStatus to always return No source (negative status indicator), even for pages that are fully previewed and published.

I can see a few options:

• somehow detect BYOM and treat explicitly differently (don't request edit in that case)
• don't quick exit when no source, proceed to rest of checks and label accordingly, something like Current, No Source
• some combination of the 2 above