Get Material Recommendations

Co-occurrence recommendation engine for the Add Item panel.

Algorithm:

1. Resolve the current list (group_name, project_id, quote_id).
2. Find peer lists: same shop AND (same group_name OR same project/quote).
3. Collect every item across those peer lists.
4. Count frequency: how many distinct lists each part_number appears in.
5. Exclude part_numbers already in the current list.
6. Return top-N by frequency, then by recency.

Also returns the 5 most recently purchased (po/purch) items from the shop as a separate "recently_ordered" list for the DefaultOverview panel.

Shop scoping is server-injected — the frontend cannot pass shop_id.