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.

doc/android-asset-validation.md

@@ -47,7 +47,7 @@ npm run build:android:studio
 #### Source Assets (Required)
 - `resources/icon.png` - App icon source
 - `resources/splash.png` - Splash screen source  
-- `resources/splash_dark.png` - Dark mode splash source
+- `resources/splash-dark.png` - Dark mode splash source
 
 #### Android Resources (Generated)
 - `android/app/src/main/res/drawable/splash.png` - Splash screen drawable
@@ -201,13 +201,13 @@ mkdir -p android/app/src/main/res/mipmap-{mdpi,hdpi,xhdpi,xxhdpi,xxxhdpi}
 # Copy source assets to assets directory
 cp resources/icon.png assets/
 cp resources/splash.png assets/
-cp resources/splash_dark.png assets/
+cp resources/splash-dark.png assets/
 
 # Generate assets manually
 npx @capacitor/assets generate
 
 # Clean up
-rm assets/icon.png assets/splash.png assets/splash_dark.png
+rm assets/icon.png assets/splash.png assets/splash-dark.png
 ```
 
 ## Future Enhancements

doc/asset-migration-plan.md

@@ -89,7 +89,7 @@ system to a standardized, single-source asset configuration approach using
 resources/                     # Image sources ONLY
   icon.png
   splash.png
-  splash_dark.png
+  splash-dark.png
 
 config/assets/                 # Versioned config & schema
   capacitor-assets.config.json