Fix stock status false positives for in-stock items

- Remove overly generic pre-order phrases that caused false positives
  ("available in", "coming in", "arriving in" matched normal text)
- Add in-stock phrase priority check - "in stock", "add to cart",
  "add to basket" now take precedence over pre-order detection
- Add Magento 2 stock status detection using stock classes and
  add-to-cart buttons
- Bump version to 1.0.2

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

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "priceghost-backend",
-  "version": "1.0.0",
+  "version": "1.0.2",
   "description": "PriceGhost price tracking API",
   "main": "dist/index.js",
   "scripts": {