[Price Compare] Step 9: Support additional suppliers beyond Metro

[frankieboxx]

Step 9 — Future Supplier Support

Currently only Metro (sifra exact match). Future plan:

• With sifra/EAN: Direct code match (any supplier using UBL e-invoicing)
• Without codes: Fuzzy name match only (lower confidence)
• Schema: add supplier field to comparison logic
• The troskovi.opis field identifies supplier (e.g., "METRO Cash & Carry d.o.o.")

File: scripts/price_compare.py
Priority: P4 — future enhancement