fix: stop protecting stale, unverified pc-builder.io catalog prices

Bug found: "Gigabyte GAMING OC GeForce RTX 5070 Ti 16 GB Video Card" kept
showing a stale price of 431.17 even after pc-builder.io itself no longer
had a fixed offer for it (its "Add to Build" HTML only had a generic
Amazon search link, no .price-box element at all, confirmed by fetching
the live page directly).

Root cause: scrapeComponentType's "never lose a better price" rule (added
to make ScrapedPartsController#compare's persisted merchant prices
durable across catalog refreshes) was too broad. It treated ANY existing
price as worth protecting whenever the incoming catalog price was null or
higher - including a price that had only ever come from a *previous*
pc-builder.io scrape itself (priceSource: null), with no independent
verification. Since pc-builder.io's own listings change constantly (a
GPU can lose its priced Amazon link if the referenced ASIN goes out of
stock), that logic effectively froze old pc-builder.io prices forever
even after the site removed them.

Fix: extracted the decision into shouldKeepExistingPrice(), which now
only protects a price when priceSource is a real merchant name (set by
updatePriceIfCheaper after a live comparison confirmed it on the
merchant's own page) - never when priceSource is null (an unverified,
previous pc-builder.io catalog price). A plain re-scrape can always
correct/clear an unverified price, matching whatever pc-builder.io
currently shows.

4 new unit tests for shouldKeepExistingPrice covering: unverified
pc-builder.io price gets overwritten (the regression case), verified
merchant price is protected from worse/missing catalog data, verified
merchant price is still replaced by a genuinely cheaper catalog price,
and no-existing-part returns false.

Also re-ran `node ace scrape:parts` to apply the fix to already-cached
data with stale unverified prices (affected ~1500 rows across the
catalog before the fix, mostly likely unaffected in practice but no
longer silently trusted going forward).

app/services/part_scraper_service.ts

@@ -251,6 +251,33 @@ async function fetchCategoryProducts(
   return rows
 }
 
+/**
+ * Decides whether a catalog refresh row should overwrite an existing
+ * ScrapedPart's price fields, or leave them untouched.
+ *
+ * Only a price that was actually *verified* via a merchant comparison
+ * (priceSource set to a merchant name by updatePriceIfCheaper, e.g.
+ * "LDLC") is protected from being overwritten by a plain catalog refresh
+ * — that price was confirmed live on the merchant's own page.
+ *
+ * A price with priceSource === null just came from a *previous*
+ * pc-builder.io catalog scrape, with no independent verification.
+ * pc-builder.io's own listings change constantly — a GPU can have a fixed
+ * Amazon price today and only a generic "search on Amazon" link (no
+ * price) tomorrow, if the ASIN it referenced runs out of stock. Treating
+ * that old, unverified pc-builder.io price as untouchable would freeze it
+ * forever even after the site itself removed it, which is exactly the
+ * bug this function fixes (a €431.17 price kept showing for a GPU
+ * pc-builder.io no longer prices at all).
+ */
+function shouldKeepExistingPrice(
+  existing: { price: number | null; priceSource: string | null } | null,
+  incomingPrice: number | null
+): boolean {
+  if (!existing || existing.price === null || existing.priceSource === null) return false
+  return incomingPrice === null || existing.price <= incomingPrice
+}
+
 /**
  * Scrapes a single component type's mapped category and upserts the
  * resulting rows into the scraped_parts cache table.
@@ -280,15 +307,7 @@ async function scrapeComponentType(
       .andWhere('sourceRef', row.sourceRef)
       .first()
 
-    // If a previous price comparison already resolved (and persisted) a
-    // real price for this part from a merchant, don't blow it away just
-    // because this catalog refresh came back with no price — keep
-    // whichever is best (see updatePriceIfCheaper for the "best of all
-    // known sources" logic used when a comparison finds a lower price).
-    const hasBetterExistingPrice =
-      existing?.price !== null &&
-      existing?.price !== undefined &&
-      (row.price === null || existing.price <= row.price)
+    const keepExistingPrice = shouldKeepExistingPrice(existing, row.price)
 
     await ScrapedPart.updateOrCreate(
       { source: SOURCE, sourceRef: row.sourceRef },
@@ -297,7 +316,7 @@ async function scrapeComponentType(
         name: row.name,
         imageUrl: row.imageUrl,
         scrapedAt,
-        ...(hasBetterExistingPrice
+        ...(keepExistingPrice
           ? {}
           : {
               price: row.price,
@@ -402,6 +421,7 @@ export {
   ensureFreshCategory,
   isCategoryStale,
   updatePriceIfCheaper,
+  shouldKeepExistingPrice,
   CATEGORY_CONFIG,
   CATEGORY_SLUGS,
   CACHE_TTL_HOURS,