chore: drop dead code, sync stale comments

- delete api/categorize.py: orphaned module, never imported. The live
  pzmm-types→category mapping is _types_to_category in mlos_sort.py.
- delete api/adapters.py:_autopick_ambiguous: 5-line wrapper around
  _apply_branch_rules with zero callers in current source.
- delete docs/backlog/polling-path-pz-build.md: described work that
  shipped — init/06_sort_jobs_pz_build.sql plus pz_build plumbing in
  jobs.create_job, app._route_to_job, and app._build_result_for_job.
- sync MAP_LINE convention comment in api/mlos_sort.py with the worker
  copy (Muldraugh, KY is appended at the end, not prepended at the
  front — see adapters.build_response:577).
- update init/04_required_wsids.sql header to reflect the authed-API
  fetch path (HTML scrape was retired in 3a34b71).
- soften the now-stale '~14 rows' count in app._strip_path_prefix's
  docstring.

init/04_required_wsids.sql

@@ -1,6 +1,8 @@
--- Required Items scraped from each mod's Steam Workshop page (the "Required
--- Items" section). Steam's anonymous GetPublishedFileDetails endpoint does
--- not include children for individual mods, so we scrape the public HTML.
+-- Required Items pulled from each mod's Steam "Required Items" sidebar.
+-- Originally scraped from the public Workshop HTML page (the anonymous
+-- GetPublishedFileDetails endpoint omits `children` for individual mods);
+-- worker.fetch_required_wsids now uses authenticated IPublishedFileService/
+-- GetDetails with includechildren=true and gets the same data structurally.
 --
 -- Use cases:
 --   1. Auto-resolving missing-dep warnings: when a cached mod_id Y is