feat: Umstellung auf Anthropic Claude SDK, Rechnungsgenerator-Systemtemplate und Task-Status-Sync

- LLM-Integration von LM Studio (Spring AI OpenAI) auf Anthropic Java SDK umgestellt
- Rechnungsgenerator: System-Template für Rechnungen an Nutzer, Canvas leeren, PDF-Vorschau
- Job manuell beenden sendet job_deleted an verbundene App-Clients
- MessageController: nur offene Jobs ausliefern, station_completed per jobId auflösen
- App: Task-Erledigungsstatus aus Server-Tasks auf Stations-Snapshots übernehmen, lokale Task-Status bei Offline-Pufferung erhalten
- Adressbuch-Wording in allen Sprachdateien, Version 0.9.18

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/lib/services/database_service.dart

@@ -116,9 +116,16 @@ class DatabaseService {
       final jobBox = _store!.box<JobEntity>();
       final taskStatusBox = _store!.box<TaskStatusEntity>();
 
-      // Clear existing jobs and related task statuses before inserting new ones
+      // Clear existing jobs before inserting new ones. Task statuses are NOT
+      // cleared wholesale: locally completed tasks may not be confirmed by the
+      // server yet (offline buffering), so only statuses of tasks that no
+      // longer exist in any job are removed below.
       jobBox.removeAll();
-      taskStatusBox.removeAll();
+
+      final existingStatuses = {
+        for (final entity in taskStatusBox.getAll()) entity.taskId: entity,
+      };
+      final knownTaskIds = <String>{};
 
       // Save new jobs
       for (final job in jobs) {
@@ -134,7 +141,8 @@ class DatabaseService {
         // Also persist task completion states from JSON (adopt status on load)
         // Only set completed=true entries to avoid overwriting local progress with false
         for (final task in normalized.tasks) {
-          if (task.completed) {
+          knownTaskIds.add(task.id);
+          if (task.completed && !existingStatuses.containsKey(task.id)) {
             final taskStatusEntity = TaskStatusEntity(
               taskId: task.id,
               completed: true,
@@ -147,6 +155,13 @@ class DatabaseService {
         }
       }
 
+      // Drop statuses of tasks that no longer belong to any assigned job
+      for (final entry in existingStatuses.entries) {
+        if (!knownTaskIds.contains(entry.key)) {
+          taskStatusBox.remove(entry.value.id);
+        }
+      }
+
       developer.log(
         'Jobs and task statuses saved successfully',
         name: 'DatabaseService',