set apart host backups of other nodes and of former jobs

- Each host backup carries the node it belongs to, read from its source host or its name (`hostcfg-<node>`, a job of this node or its PBS backup ID); both backup lists also return the node name.
- The backup list offers This node / All nodes when some backup belongs to another node, with This node as the default, a count that follows the choice and a note with the backups not shown.
- Backups whose node cannot be read from their name are listed under All nodes.
- A local backup made on this node by a job that no longer exists is marked as Former job, read from its metadata file; backups without it, manual ones and those of other nodes are not marked.
- New texts in English and Spanish, modelled in the translation steady-state test.
- Tests for the node and the former job read from each backup, and for the cluster node membership notifications.

.github/scripts/tests/test_command_descriptions.py

@@ -99,6 +99,13 @@ class CommandDescriptionsTests(unittest.TestCase):
                     temporary = json.loads(path.read_text())
                     for section, key in (
                         ("archives", "emptyMessage"),
+                        ("archives", "formerJob"),
+                        ("archives", "formerJobTitle"),
+                        ("archives", "hiddenOtherNodes"),
+                        ("archives", "scopeAllNodes"),
+                        ("archives", "scopeAriaLabel"),
+                        ("archives", "scopeShowAll"),
+                        ("archives", "scopeThisNode"),
                         ("destinations", "backupsKeptMessage"),
                         ("destinations", "localAttachHelpMessage"),
                     ):