sync: fix PDF candidate selection to consider all PDFs and prefer main.pdf/paper.pdf at root

fix: replace executor on cancel to unblock new pipeline runs

debug: add trace prints to upload route to find hang point

fix: log google auth error reason; export pipeline env vars in start.sh

Add itagpdf.com to CORS allowed origins

Sync latest backend and pipeline code

fix: remove pipeline cancellation so concurrent users queue instead of cancel

Initial deployment