Merge develop: combine the i18n test fixture with #363

Both message batches seeded locale copies at the same point of
test_command_descriptions.py. The two blocks are independent — one
seeds the backup messages, the other the storage ones — so they are
merged into a single block that reads and writes the fixture once.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

AppImage/messages/en/common.json

@@ -3835,6 +3835,7 @@
       "downloadTitle": "Download this backup",
       "emptyAfter": "backups yet.",
       "emptyBefore": "No",
+      "emptyMessage": "No backup archives found.",
       "encrypted": "Encrypted",
       "encryptedTitle": "This backup is encrypted",
       "filesInBackup": "Files in backup",
@@ -3910,6 +3911,7 @@
       "addPbsRepository": "Add PBS repository",
       "appendAuthorizedKeyBefore": "Append the generated public key to",
       "backupsKeptBefore": "Existing backups are kept in",
+      "backupsKeptMessage": "Existing backup archives are not deleted.",
       "borgEncryptionInherited": "Borg encryption is controlled by the repository.",
       "builtIn": "Built-in",
       "builtInDefault": "Built-in default",
@@ -3930,6 +3932,7 @@
       "leavePassphraseBlank": "Leave blank to keep the saved passphrase.",
       "leavePasswordBlank": "Leave blank to keep the saved password.",
       "localAttachHelpBefore": "Use a mounted local path. For USB drives, mount them first in",
+      "localAttachHelpMessage": "Mount USB drives first. Leave blank to use the PVE storage path + /dump (fallback: /var/lib/vz/dump).",
       "localAttachHelpMiddle": "USB drives",
       "localManualPickHelp": "Pick a local path for one-shot backup output.",
       "localPathHelpAfter": "or another mounted path.",