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.

api/adapters.py

@@ -552,13 +552,6 @@ def _apply_branch_rules(
 
 # Backwards-compat shim used by existing call sites that don't yet pass
 # pz_build/input_modids. Removed once all callers migrate.
-def _autopick_ambiguous(mods: List[ModInfo]) -> Tuple[Set[str], List[Dict[str, Any]]]:
-    drop_ids, warns, _hints = _apply_branch_rules(
-        mods, pz_build="B42", input_modids={m.id for m in mods},
-    )
-    return (drop_ids, warns)
-
-
 def build_response(
     input_ids: List[str],
     hit_ids: List[str],