feat(frontend+billing): integrate billing UI and navigation into Turnier module

- **Navigation Updates:**
  - Added `AppScreen.Billing` route for participant billing linked to an event and tournament.

- **UI Additions:**
  - Introduced `BillingScreen` and `BillingViewModel` for participant account management and manual transactions.
  - Updated `TurnierAbrechnungTab` to include `BillingScreen` and enable account interaction.

- **Turnier Enhancements:**
  - Enhanced `NennungenTabContent` to support navigation to billing via a new interaction.
  - Added billing feature as a dependency to `turnier-feature`.

- **Billing Domain:**
  - Extended `Money` to include subtraction operation and improved formatting for negative amounts.
  - Added DTOs (`TeilnehmerKontoDto`, `BuchungDto`, `BuchungRequest`) for seamless data exchange with backend.

- **Test Improvements:**
  - Updated `PreviewTurnierAbrechnungTab` to include interactive billing placeholder.

- **Misc Updates:**
  - Enhanced breadcrumb navigation for billing in `DesktopMainLayout` for better user experience.

frontend/shells/meldestelle-desktop/src/jvmMain/kotlin/at/mocode/desktop/screens/layout/DesktopMainLayout.kt

@@ -10,12 +10,8 @@ import androidx.compose.material.icons.filled.Devices
 import androidx.compose.material.icons.filled.Wifi
 import androidx.compose.material.icons.filled.WifiOff
 import androidx.compose.material3.*
-import androidx.compose.runtime.Composable
-import androidx.compose.runtime.getValue
-import androidx.compose.runtime.mutableStateOf
-import androidx.compose.runtime.remember
+import androidx.compose.runtime.*
 import androidx.compose.runtime.saveable.rememberSaveable
-import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
@@ -23,6 +19,8 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import at.mocode.frontend.core.navigation.AppScreen
+import at.mocode.frontend.features.billing.presentation.BillingScreen
+import at.mocode.frontend.features.billing.presentation.BillingViewModel
 import at.mocode.frontend.features.profile.presentation.ProfileScreen
 import at.mocode.frontend.features.profile.presentation.ProfileViewModel
 import at.mocode.frontend.features.verein.presentation.VereinScreen
@@ -31,7 +29,6 @@ import at.mocode.ping.feature.presentation.PingScreen
 import at.mocode.ping.feature.presentation.PingViewModel
 import at.mocode.turnier.feature.presentation.TurnierDetailScreen
 import at.mocode.veranstalter.feature.presentation.FakeVeranstalterStore
-import at.mocode.veranstalter.feature.presentation.VeranstalterNeuScreen
 import at.mocode.veranstaltung.feature.presentation.AdminUebersichtScreen
 import at.mocode.veranstaltung.feature.presentation.VeranstaltungDetailScreen
 import at.mocode.veranstaltung.feature.presentation.VeranstaltungNeuScreen
@@ -237,6 +234,33 @@ private fun DesktopTopBar(
             fontWeight = FontWeight.SemiBold,
           )
         }
+        is AppScreen.Billing -> {
+          BreadcrumbSeparator()
+          Text(
+            text = "Veranstaltung #${currentScreen.veranstaltungId}",
+            color = TopBarTextColor.copy(alpha = 0.75f),
+            fontSize = 14.sp,
+            modifier = Modifier.clickable {
+              onNavigate(AppScreen.VeranstaltungProfil(0, currentScreen.veranstaltungId))
+            },
+          )
+          BreadcrumbSeparator()
+          Text(
+            text = "Turnier ${currentScreen.turnierId}",
+            color = TopBarTextColor.copy(alpha = 0.75f),
+            fontSize = 14.sp,
+            modifier = Modifier.clickable {
+              onNavigate(AppScreen.TurnierDetail(currentScreen.veranstaltungId, currentScreen.turnierId))
+            },
+          )
+          BreadcrumbSeparator()
+          Text(
+            text = "Abrechnung",
+            color = TopBarTextColor,
+            fontSize = 14.sp,
+            fontWeight = FontWeight.SemiBold,
+          )
+        }
         is AppScreen.TurnierNeu -> {
           BreadcrumbSeparator()
           Text(
@@ -630,6 +654,16 @@ private fun DesktopContentArea(
       )
     }
 
+    // --- Billing ---
+    is AppScreen.Billing -> {
+      val billingViewModel: BillingViewModel = koinViewModel()
+      BillingScreen(
+        viewModel = billingViewModel,
+        veranstaltungId = currentScreen.veranstaltungId,
+        onBack = onBack
+      )
+    }
+
     // Fallback → Root
     else -> AdminUebersichtScreen(
       onVeranstalterAuswahl = { onNavigate(AppScreen.VeranstalterAuswahl) },

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

@@ -151,7 +151,7 @@ fun PreviewTurnierArtikelTab() {
 @Composable
 fun PreviewTurnierAbrechnungTab() {
   MaterialTheme {
-    AbrechnungTabContent()
+    AbrechnungTabContent(veranstaltungId = 1L)
   }
 }