Get Finra Short Interest Debug

Upfront diagnostic (same lesson learned this whole session): the one part of this collector that couldn't be verified from the sandbox is which candidate settlement-date file actually exists on FINRA's CDN right now, and whether its column headers match either of the two schema generations this parser tries. Returns the raw HTTP status for EVERY candidate date tried (not just the first success), plus the raw header row and first data row of whichever one worked.