gwshop: count dump coverage by unique objectID (review fixes)

Summed nbHits across facet branches double-counted products listed in
several branches; coverage is now per unique objectID, with a warning
about records left out of the dump. AGENTS.md documents the live
count (4183 records, 3491 via facet).

AGENTS.md

@@ -227,11 +227,14 @@ never re-fetch them again):
    key is search-only, never commit any other Algolia key. The full
    product index `prod-lazarus-product-en-ww` (~3500 products, plus one
    sibling index per locale) is dumped with plain `requests`: the
-   search-only key cannot use Algolia's `/browse` (403) and normal
+   public search-only key cannot use Algolia's `/browse` (403) and normal
    pagination is capped at 1000 cumulative hits, so `gwshop.py`
    **partitions the index on the `GameSystemsRoot` hierarchical facet** —
    each branch is fetched with an explicit filter, recursing deeper only
-   when a branch exceeds one page. Records are normalized into the
+   when a branch exceeds one page. (Live count 2026-10-04: 4183 records,
+   of which 3491 are reachable via the facet; the ~692 left out are paints,
+   Black Library books, White Dwarf issues, brushes, bases and gifts that
+   carry no `GameSystemsRoot` path — no miniature kits among them.) Records are normalized into the
    source-agnostic catalog schema (system/group/faction/subfaction/class
    = the facet path, name/sku/productType attached) into
    `data/gwshop_catalog.json`, which is the sorter's default catalog and