fix: handle prodapi response field variants

[oliyy]

Summary

• tolerate PCHome prodapi integer fields returned as quoted numeric strings, numbers, or nulls
• preserve field-level decode errors instead of reporting every decode failure as an unexpected response shape
• add regression coverage for observed product and button payload variants

Root cause

PCHome still returns a keyed product object, but selected fields such as Price.Low and Qty can now vary between JSON numbers, strings, and nulls depending on the product.

Validation

• go test ./...
• verified the reported live searches return without product enrichment warnings