feat(core+frontend): add P2P sync infrastructure with WebSocket support

- **Core Updates:**
  - Implemented `P2pSyncService` interface with platform-specific WebSocket implementations (`JvmP2pSyncService` and no-op for JS).
  - Developed `SyncEvent` sealed class hierarchy to handle peer synchronization events (e.g., `PingEvent`, `PongEvent`, `DataChangedEvent`, etc.).

- **Frontend Integration:**
  - Introduced `SyncManager` to manage peer discovery and synchronization, coupled with `NetworkDiscoveryService`.
  - Updated dependency injection to include `syncModule` for platform-specific sync service initialization.
  - Enhanced `BewerbViewModel` to support new sync capabilities, including observing sync events and UI updates for connected peers.

- **Backend Enhancements:**
  - Added ZNS-specific fields (`zns_nummer`, `zns_abteilung`) to Bewerb table for idempotent imports.
  - Introduced import ZNS logic to handle duplicates and align with SyncManager updates.

- **UI Improvements:**
  - Enhanced `TurnierBewerbeTab` with updated dialogs (ZNS imports, sync status) and dynamic previews.
  - Improved network syncing feedback and error handling in frontend components.

- **DB Changes:**
  - Added migration for new column fields in the Bewerb table with relevant indexing for ZNS import optimizations.

backend/services/entries/entries-service/src/main/resources/db/tenant/V7__add_bewerb_zns_fields.sql

@@ -0,0 +1,9 @@
+-- V7: ZNS-spezifische Felder für Bewerbe zur Vermeidung von Duplikaten beim Import
+-- Context: Phase 8 – ZNS Importer Erweiterung
+
+ALTER TABLE bewerbe
+  ADD COLUMN IF NOT EXISTS zns_nummer     INTEGER NULL,
+  ADD COLUMN IF NOT EXISTS zns_abteilung  INTEGER NULL;
+
+-- Index für schnelles Nachschlagen beim Import
+CREATE INDEX IF NOT EXISTS idx_bewerbe_zns_ref ON bewerbe(turnier_id, zns_nummer, zns_abteilung);