Rename app to 'tiptoi Sync' and add tiptoi pen icon/splash screens

- App display name: 'TipToi Sync' -> 'tiptoi Sync' (strings.xml,
  capacitor.config.ts).
- New app icon: stylized tiptoi pen (orange body, grip band, sensor
  tip) on dark background, regenerated for all mipmap densities plus
  the adaptive icon foreground and round variant.
- Matching splash screens (portrait + landscape, all densities) with
  the same pen motif centered on the dark background.
- Web favicon updated to match.
- Removed unused legacy vector icon assets
  (drawable/ic_launcher_background.xml,
  drawable-v24/ic_launcher_foreground.xml) that were superseded by the
  raster icons.

client/capacitor.config.ts

@@ -6,7 +6,7 @@ const devUrl = process.env.DEV_URL
 
 const config: CapacitorConfig = {
   appId: 'com.tiptoisync.app',
-  appName: 'TipToi Sync',
+  appName: 'tiptoi Sync',
   webDir: 'dist',
   server: devUrl
     ? { url: devUrl, cleartext: true }