chore(branding): Anzeigename 'Holzleitner Auslieferung' + Launcher-Icon

- Android android:label, iOS CFBundleDisplayName, MaterialApp.title -> 'Holzleitner Auslieferung'
- flutter_launcher_icons (assets/launch_icon.png) als Dev-Dep + Config

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

android/app/src/main/AndroidManifest.xml

@@ -15,7 +15,7 @@
     <uses-permission android:name="android.permission.INTERNET" />
 
     <application
-        android:label="hl_lieferservice"
+        android:label="Holzleitner Auslieferung"
         android:name="${applicationName}"
         android:icon="@mipmap/ic_launcher"
         android:networkSecurityConfig="@xml/network_security_config">