refactor(ui, navigation): implement platform-specific routing and redesign components

- Added platform detection logic `currentPlatform()` in `PlatformType.js.kt`.
- Introduced platform-based behavior for LandingScreen, Dashboard, and Login flow.
- Replaced Row with FlowRow in PingScreen to improve button layout.
- Updated Meldestelle Dashboard with platform-specific headers and authentication checks.
- Adjusted AppHeader to accept `isAuthenticated` and `username` parameters.

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

frontend/shells/meldestelle-portal/src/jvmMain/kotlin/main.kt

@@ -40,7 +40,7 @@ fun main() = application {
   }
   Window(
     onCloseRequest = ::exitApplication,
-    title = "Equest-Events Master Desktop",
+    title = "Master Desktop",
     state = WindowState(width = 1200.dp, height = 800.dp)
   ) {
     MainApp()