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 };