Remove meta-refresh fallback from backfill loading page
The SSE-driven progress bar already navigates the user to their profile
as soon as the backfill row hits a terminal state; the 15s meta-refresh
was reloading the loading page in parallel, which is redundant when SSE
works and unhelpful when it doesn't (it just resets a potentially-
recoverable in-progress backfill).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>