Duplicate re-published entries dropped; bulk releases get summaries

Fixed

• Duplicate entries from re-publishing changelogs — when a source republishes the same content under a new title or anchor URL, the duplicate is now dropped; release candidates, backports, and sibling packages that ship identical notes are linked as related coverage instead.
• App Store "bug fixes and performance improvements" releases no longer receive AI-generated summaries; sources configured to opt out of summarization now have that setting honored consistently on every write path.
• Changelog sources with long publication histories now update reliably — a database parameter limit was causing ingest jobs to fail silently on active feeds.
• Bulk-published releases (via the GitHub Actions publisher or the batch API) now receive AI headlines and summaries; previously, batches of more than 20 items silently skipped the summarization pass.
• Connecting apps via OAuth now works correctly with discovery-based clients — the server's discovery document now accurately reflects the authorization code + PKCE flow that self-registering clients use, so clients that read it before registering no longer fail at the token exchange step.