fix: logo not showing and duplicate ProsApp text in auth layout

- Put logo inside white container on gradient so colors are correct
- Remove BlendMode.srcATop which was making logo invisible on gradient
- Simplify auth_layout mobile/desktop branches

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

lib/ui/layouts/auth/widgets/background_auth.dart

@@ -16,14 +16,20 @@ class BackgroundAuth extends StatelessWidget {
       child: Column(
         mainAxisAlignment: MainAxisAlignment.center,
         children: [
-          Image.network(
-            'https://prosapp.co/img/logo_prosapp.png',
-            width: 180,
-            color: Colors.white,
-            colorBlendMode: BlendMode.srcATop,
-            errorBuilder: (_, __, ___) => const Text(
-              'ProsApp',
-              style: TextStyle(fontSize: 36, fontWeight: FontWeight.bold, color: Colors.white),
+          Container(
+            padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 14),
+            decoration: BoxDecoration(
+              color: Colors.white,
+              borderRadius: BorderRadius.circular(16),
+            ),
+            child: Image.network(
+              'https://prosapp.co/img/logo_prosapp.png',
+              height: 48,
+              fit: BoxFit.contain,
+              errorBuilder: (_, __, ___) => const Text(
+                'ProsApp',
+                style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold, color: Color(0xFF42A4EF)),
+              ),
             ),
           ),
           const SizedBox(height: 24),