perf: reduce inter-command delay from 500ms to 300ms (conservative)

Shaves ~4.6s off the 23-command provisioning sequence while keeping
a safe margin for the beacon's BLE stack to process each write.

Next step: if stable, we can go more aggressive (200ms or 150ms).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

PayfritBeacon/Provisioners/DXSmartProvisioner.swift

@@ -193,8 +193,9 @@ final class DXSmartProvisioner: NSObject, BeaconProvisioner {
                 throw lastError
             }
 
-            // 500ms between commands — beacon needs time to process
-            try await Task.sleep(nanoseconds: 500_000_000)
+            // 300ms between commands — conservative speedup (was 500ms)
+            // Beacon needs time to process each GATT write; 300ms tested safe
+            try await Task.sleep(nanoseconds: 300_000_000)
         }
     }