Add ONVIF probe detector via unicast WS-Discovery

- Add ProbeONVIF() prober: sends unicast WS-Discovery to ip:3702,
  parses XAddrs, Name, Hardware from response (no auth needed)
- Add ONVIFResult struct to probe models
- Register ONVIF detector with highest priority (before HomeKit)
- Fix homekit.html back-wrapper max-width to match design system

www/homekit.html

@@ -60,13 +60,13 @@
         .back-wrapper {
             position: absolute; top: 1.5rem;
             left: 50%; transform: translateX(-50%);
-            width: 100%; max-width: 480px;
+            width: 100%; max-width: 600px;
             padding: 0 1.5rem;
             z-index: 10;
         }
 
         @media (min-width: 768px) {
-            .back-wrapper { max-width: 540px; }
+            .back-wrapper { max-width: 660px; }
         }
 
         .btn-back {