Batch-resolve messy vendor names to catalog ids

Batch-resolve a pasted/messy vendor list (e.g. an AP-export column) to catalog vendor_ids in one call. A READ (it never mutates state — hence NOT consequential) that takes an array body. Per submitted name returns { submitted, status, confidence, resolved_vendor_id?, resolved_name?, candidates? } where status is 'resolved' (high-confidence — use the id directly), 'ambiguous' (several close matches — show the dealer the candidates), or 'unresolved' (no confident match — do NOT invent a vendor). Resolve the whole list, THEN POST /stack/vendors per resolved row with its vendor_id + monthly_cost. Conservative on purpose: a wrong auto-match is worse than unresolved, and the no-free-text moat holds on the write side regardless.