feat(core+frontend): integrate mDNS-based network discovery and update UI

- **Network Discovery Service:**
  - Added platform-specific `DiscoveryModule` with JmDNS-based `JmDnsDiscoveryService` for JVM and no-op implementation for JS.
  - Implemented service and device discovery using mDNS to enable peer-to-peer synchronization within LAN.
  - Registered the module in Koin for dependency injection and integrated it with `networkModule`.

- **Frontend Integration:**
  - Enhanced `BewerbViewModel` with intents and actions for starting, stopping, and refreshing network scans.
  - Introduced polling for discovered services during an active scan.

- **UI Additions:**
  - Added a `NetworkDiscoveryPanel` in `TurnierBewerbeTab` to display discovered services and indicate scan state.
  - Updated action buttons to include toggle functionality for network scans.

frontend/shells/meldestelle-desktop/src/jvmMain/kotlin/at/mocode/desktop/screens/preview/ScreenPreviews.kt

@@ -128,7 +128,7 @@ fun PreviewTurnierBewerbeTab() {
     override suspend fun generate(bewerbId: Long): Result<List<StartlistenZeile>> = Result.success(emptyList())
     override suspend fun getByBewerb(bewerbId: Long): Result<List<StartlistenZeile>> = Result.success(emptyList())
   }
-  val vm = BewerbViewModel(mockRepo, mockStartlistenRepo, 1L)
+  val vm = BewerbViewModel(mockRepo, mockStartlistenRepo, null, 1L)
   MaterialTheme {
     BewerbeTabContent(viewModel = vm, turnierId = 1L)
   }