Background tasks (ingestion, PDF resolution, scheduler) now acquire an
asyncio.Semaphore before checking out a DB connection, guaranteeing at
least N connections remain available for API request handlers. Removes
duplicate polling loop from PublicationsPage, debounces publication
reload on run-status changes, and increases poll interval from 5s to 15s
since SSE handles live discovery.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
