Return the calling user's personal dogfood interview link for this topic, plus the latest test interview they have recorded against it. Lazily get-or-creates a per-caller IntervieweeContext + enabled SharingConfiguration the first time it's called, then returns the same stable URL on subsequent calls. The caller's identifier is intentionally not added to the topic's targeting arrays — each user dogfoods under their own row, so test calls never mint a public share token on someone else's behalf.