feat(backup): option to back up on every exit, not just once a day

New BackupSettings.EveryExit (keyBackupEveryExit) with a Settings → Backup
checkbox. When on, the three shutdown-backup gates (plannedShutdownSteps,
runBackupForShutdown, maybeShutdownBackup) bypass the HasBackupToday /
HasADIFBackupToday "already done today" check and always run, so a second
session's QSOs are captured instead of skipped until the next day. The dated
backup file for today is refreshed (overwritten) each exit; prior days are still
kept by rotation.

changelog.json

@@ -2,8 +2,12 @@
   {
     "version": "0.23.9",
     "date": "",
-    "en": [],
-    "fr": []
+    "en": [
+      "Backup: new \"Back up on every exit\" option (Settings → Backup). With it on, OpsLog backs up the database each time you quit instead of only the first time of the day — so a second session's QSOs are always captured."
+    ],
+    "fr": [
+      "Sauvegarde : nouvelle option \"Sauvegarder à chaque fermeture\" (Réglages → Sauvegarde). Activée, OpsLog sauvegarde la base à chaque fois que tu quittes au lieu d'une seule fois par jour — les QSO d'une seconde session sont ainsi toujours pris."
+    ]
   },
   {
     "version": "0.23.8",