fix: Profile duplication on device connect

DeviceKey resolver was falling back to deviceId when publicKey wasn't
yet available during early connection. This created two different keys
(id:xxx then pk:yyy) for the same device, causing a new profile to be
created each time.

Now returns null until publicKey is available, so profile sync waits
for the stable identifier.

lib/services/profile_device_key_resolver.dart

@@ -5,25 +5,17 @@ class ProfileDeviceKeyResolver {
     required DeviceInfo deviceInfo,
     required ConnectionMode connectionMode,
   }) {
+    // Always prefer the public key — it's the only truly stable identifier.
+    // Don't fall back to deviceId to avoid creating duplicate profiles when
+    // publicKey arrives late (after initial connection but before DeviceInfo).
     final publicKey = deviceInfo.publicKey;
-    if (publicKey != null && publicKey.isNotEmpty) {
+    if (publicKey == null || publicKey.isEmpty) {
+      return null; // Wait until publicKey is available
+    }
+
     final hex = publicKey
         .map((byte) => byte.toRadixString(16).padLeft(2, '0'))
         .join();
-      if (hex.isNotEmpty) {
-        return 'pk:$hex';
-      }
-    }
-
-    final deviceId = deviceInfo.deviceId?.trim();
-    if (deviceId == null || deviceId.isEmpty) {
-      return null;
-    }
-
-    if (connectionMode == ConnectionMode.usb && deviceId == 'usb') {
-      return null;
-    }
-
-    return 'id:$deviceId';
+    return hex.isNotEmpty ? 'pk:$hex' : null;
   }
 }