fix(assets): rename splash_dark.png to splash-dark.png

Match the filename @capacitor/assets expects so iOS uses the custom
dark splash instead of the logo-on-black fallback.

scripts/assets-config.ts

@@ -92,7 +92,7 @@ function generateAssetConfig(): AssetConfig {
     },
     splash: {
       source: "resources/splash.png",
-      darkSource: "resources/splash_dark.png",
+      darkSource: "resources/splash-dark.png",
       android: {
         scale: "cover",
         target: "android/app/src/main/res"
@@ -138,7 +138,7 @@ function validateSourceFiles(): void {
   const requiredFiles = [
     'resources/icon.png',
     'resources/splash.png',
-    'resources/splash_dark.png'
+    'resources/splash-dark.png'
   ];
 
   const missingFiles = requiredFiles.filter(file => {