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/features/turnier-feature/src/jvmMain/kotlin/at/mocode/turnier/feature/presentation/TurnierAbrechnungTab.kt

@@ -16,6 +16,9 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import at.mocode.frontend.core.designsystem.models.PlaceholderContent
+import at.mocode.frontend.features.billing.presentation.BillingScreen
+import at.mocode.frontend.features.billing.presentation.BillingViewModel
+import org.koin.compose.koinInject
 
 private val PrimaryBlue = Color(0xFF1E3A8A)
 private val AccentBlue = Color(0xFF3B82F6)
@@ -30,7 +33,19 @@ private val OffenePostenRot = Color(0xFFDC2626)
  * - Rechte Sidebar: Suche nach Reiter/Pferd, Zahlungsart, Buchen-Button
  */
 @Composable
-fun AbrechnungTabContent() {
+fun AbrechnungTabContent(veranstaltungId: Long) {
+  val billingViewModel: BillingViewModel = koinInject()
+
+  BillingScreen(
+    viewModel = billingViewModel,
+    veranstaltungId = veranstaltungId,
+    onBack = {}
+  )
+}
+
+/* Alter Inhalt auskommentiert oder entfernt */
+@Composable
+private fun LegacyAbrechnungTabContent() {
   var subTab by remember { mutableIntStateOf(0) }
   var sidebarTab by remember { mutableIntStateOf(2) } // BUCHUNGEN default
   val subTabs = listOf("BUCHUNGEN", "OFFENE POSTEN", "RECHNUNG")

frontend/features/turnier-feature/src/jvmMain/kotlin/at/mocode/turnier/feature/presentation/TurnierDetailScreen.kt

@@ -103,8 +103,8 @@ fun TurnierDetailScreen(
             Text("BEWERBE Tab (Anbindung in Arbeit)", modifier = Modifier.align(Alignment.Center))
         }
         3 -> ArtikelTabContent()
-        4 -> AbrechnungTabContent()
-        5 -> NennungenTabContent()
+        4 -> AbrechnungTabContent(veranstaltungId = veranstaltungId)
+        5 -> NennungenTabContent(onAbrechnungClick = { selectedTab = 4 })
         6 -> StartlistenTabContent()
         7 -> ErgebnislistenTabContent()
       }

frontend/features/turnier-feature/src/jvmMain/kotlin/at/mocode/turnier/feature/presentation/TurnierNennungenTab.kt

@@ -30,7 +30,7 @@ private val NennSelectedBg = Color(0xFFEFF6FF)
  *  - Rechts (360dp):  Verkauf/Buchungen + Bewerbsübersicht
  */
 @Composable
-fun NennungenTabContent() {
+fun NennungenTabContent(onAbrechnungClick: () -> Unit = {}) {
   Row(modifier = Modifier.fillMaxSize()) {
     // ── Linke Spalte: Suche + Tabelle ─────────────────────────────────────
     Column(modifier = Modifier.weight(1f).fillMaxHeight()) {
@@ -48,7 +48,7 @@ fun NennungenTabContent() {
         .fillMaxHeight()
         .verticalScroll(rememberScrollState()),
     ) {
-      VerkaufBuchungenPanel()
+      VerkaufBuchungenPanel(onAbrechnungClick)
       HorizontalDivider()
       BewerbsuebersichtPanel()
     }
@@ -170,9 +170,18 @@ private fun NennungStatusBadge(status: String) {
 }
 
 @Composable
-private fun VerkaufBuchungenPanel() {
+private fun VerkaufBuchungenPanel(onAbrechnungClick: () -> Unit = {}) {
   Column(modifier = Modifier.padding(12.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
-    Text("Verkauf / Buchungen", fontWeight = FontWeight.SemiBold, fontSize = 13.sp)
+    Row(
+      modifier = Modifier.fillMaxWidth(),
+      horizontalArrangement = Arrangement.SpaceBetween,
+      verticalAlignment = Alignment.CenterVertically
+    ) {
+      Text("Verkauf / Buchungen", fontWeight = FontWeight.SemiBold, fontSize = 13.sp)
+      TextButton(onClick = onAbrechnungClick) {
+        Text("Zur Abrechnung", fontSize = 11.sp, color = NennBlue)
+      }
+    }
 
     // Artikel-Buchungen
     Card(elevation = CardDefaults.cardElevation(defaultElevation = 1.dp)) {