Add watchdog for missed launchd runs, add backup retention

Mirrors the same fix on the Lotto sibling project. watchdog.py
(com.eurojackpot.watchdog.plist, daily 09:00) checks whether the
latest draw or trained models are older than the launchd schedule
allows and alerts via EurojackpotNotifier.send_error() - catches a
silently-missed StartCalendarInterval run (e.g. Mac asleep at the
scheduled time) that launchd itself never retries.

EurojackpotAPIUpdater.create_backup() didn't have Lotto's path bug,
but had the same unbounded growth (85 backups, 2.4MB accumulated).
Adds retention (keep last 30) and prunes the existing backlog.

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

scripts/utils/update_from_api.py

@@ -91,7 +91,7 @@ class EurojackpotAPIUpdater:
             return False
 
     def create_backup(self) -> bool:
-        """Erstellt Backup."""
+        """Erstellt Backup und behält nur die letzten KEEP_BACKUPS Stück."""
         if not os.path.exists(self.data_file):
             return True
 
@@ -108,12 +108,28 @@ class EurojackpotAPIUpdater:
             shutil.copy2(self.data_file, self.backup_file)
             print(f"   ✅ Backup: {os.path.basename(self.backup_file)}")
 
+            self._prune_old_backups(backup_dir, filename)
+
             return True
 
         except Exception as e:
             print(f"   ⚠️  Backup-Fehler: {e}")
             return False
 
+    @staticmethod
+    def _prune_old_backups(backup_dir: str, filename: str, keep: int = 30) -> None:
+        """Behält nur die KEEP neuesten Backups, löscht den Rest."""
+        pattern = f"{filename}.backup_"
+        backups = sorted(
+            (f for f in os.listdir(backup_dir) if f.startswith(pattern)),
+            reverse=True,
+        )
+        for old in backups[keep:]:
+            try:
+                os.remove(os.path.join(backup_dir, old))
+            except OSError:
+                pass
+
     def fetch_from_api(self, api_name: str) -> List[Dict]:
         """
         Holt Daten von spezifischer API.