Restore 3 concurrent batches with Haiku; recalibrate progress bar

Haiku has generous rate limits so parallelism is safe again. Retry
logic catches any 429s. Progress estimate updated to ~8s per wave.

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

src/PowderCoating.Infrastructure/Services/AiCatalogPriceCheckService.cs

@@ -22,7 +22,7 @@ public class AiCatalogPriceCheckService : IAiCatalogPriceCheckService
 
     private const string Model = "claude-haiku-4-5-20251001";
     private const int BatchSize = 25;
-    private const int MaxConcurrentBatches = 1; // Tier 1 output limit is 8,000 TPM — sequential avoids bursting past it
+    private const int MaxConcurrentBatches = 3; // Haiku has generous rate limits; retry logic handles any 429s
     private const int RateLimitRetrySeconds = 65; // wait just past the 60s window before retrying a 429
 
     private static readonly JsonSerializerOptions JsonOpts = new() { PropertyNameCaseInsensitive = true };

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

@@ -11,10 +11,11 @@
     if (!form || !btn || !overlay) return;
 
     // Estimate total seconds based on item count.
-    // Batches run sequentially (1 at a time) at roughly 18s each.
+    // Haiku: 3 concurrent batches, ~8s per wave.
     function estimateDuration(itemCount) {
         var batches = Math.max(1, Math.ceil(itemCount / 25));
-        return Math.max(30, batches * 18);
+        var waves = Math.ceil(batches / 3);
+        return Math.max(15, waves * 8);
     }
 
     // Messages keyed to approximate progress milestones (0–100).