Fix progress bar timing for sequential batch processing

Was still estimating based on 3 concurrent waves (old model).
Sequential mode runs ~18s per batch, so 500 items ≈ 6 minutes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/wwwroot/js/catalog-price-check.js

@@ -10,12 +10,11 @@
 
     if (!form || !btn || !overlay) return;
 
-    // Estimate total seconds based on item count (roughly 12s per batch of 25, min 15s).
+    // Estimate total seconds based on item count.
+    // Batches run sequentially (1 at a time) at roughly 18s each.
     function estimateDuration(itemCount) {
-        // 25 items/batch, up to 3 concurrent — wall time ≈ ceil(batches/3) × 12s
         var batches = Math.max(1, Math.ceil(itemCount / 25));
-        var waves = Math.ceil(batches / 3);
-        return Math.max(15, waves * 12);
+        return Math.max(30, batches * 18);
     }
 
     // Messages keyed to approximate progress milestones (0–100).