fix(sync): stop full-catalog package wipe, enrich-stub 404s, and O(n·m) bulk deletes

Three bugs surfaced by a monitored 'sync --full' run:

- sync --full's update step ran without ctx.fullSync, so the packages
  adapter resolved 'official' scope and tombstoned all 11k previously
  synced SwiftPackageIndex pages as stale (the crawl phase then re-fetched
  them from scratch). Thread fullSync into the update step, and mark
  official-scope discovery as partial so a subset inventory can never
  tombstone pages outside its scope (also fixes the standalone update
  command permanently wiping the catalog).

- The Xcode-asset enricher matched corpus keys exactly, but the asset
  strips apostrophes from article slugs, so pages like
  metal/using-metal-to-draw-a-view's-contents were re-inserted as novel
  contentless duplicates under slugs that 404 publicly — and sample-code
  discovery trusted every role='sampleCode' document, producing guaranteed
  'Fetch failed' warnings on every sync with no path to converge. Match
  apostrophe-insensitively in the enricher and skip enrichedFrom documents
  in sample-code discovery.

- Deleting a document scans document_relationships (2.2M rows) for
  to_key = ? since v21 dropped idx_rel_to; the stale loop did that once
  per page in its own transaction — ~24B row visits for the 11k batch,
  pinning the sync at 99% CPU for tens of minutes. Add markPagesDeleted:
  one transaction, transient to_key index for the batch, dropped after.