Replaced simple exact-match with 8-layer fallback strategy:
1. Exact normalized part number (parts.oem_part_number)
2. Exact normalized aftermarket part number
3. Exact normalized cross-reference number
4. Partial ILIKE match on OEM numbers
5. Partial ILIKE match on aftermarket numbers
6. Partial ILIKE match on cross-reference numbers
7. Separator-stripped fallback (KYB-343412 → KYB343412)
8. Name-based search on parts.name_part / parts.name_es
and aftermarket_parts.name_aftermarket_parts when no part_number hit
Brand-aware filtering: when brand hint is provided and not 'GENERAL',
only returns MYEs for vehicles of that brand.
Limits: max 20 part IDs per layer, max 200 MYEs total.
Test: BPR5ES + TOYOTA → matched True, 2 parts, 200 MYEs inserted.