Fix anchor price selection - prioritize anchor over method

The previous logic checked preferred method first, which could select
a wrong price even when anchor price was available. Now:

1. PRIORITY 1: Anchor price - if user confirmed a price, find closest
   match (within 10% tolerance) across ALL candidates
2. PRIORITY 2: Preferred method - only used if no anchor match found
3. PRIORITY 3: Consensus voting

Also added debug logging to trace anchor price saving and retrieval.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/routes/products.ts

@@ -59,6 +59,7 @@ router.post('/', async (req: AuthRequest, res: Response) => {
 
       // Store the anchor price - used on refresh to select the correct variant
       await productQueries.updateAnchorPrice(product.id, selectedPrice);
+      console.log(`[Products] Saved anchor price ${selectedPrice} for product ${product.id} (method: ${selectedMethod})`);
 
       // Record the user-selected price
       await priceHistoryQueries.create(