feat(cli): status shows last export age

Reads .relicario/last_backup (written by cmd_backup_export). Format:
'never' for fresh vaults, '4 days ago' otherwise. Closes the
'is my backup stale?' question without leaving the terminal.

crates/relicario-cli/tests/settings.rs

@@ -109,6 +109,32 @@ fn status_reports_item_attachment_and_device_counts() {
     );
 }
 
+#[test]
+fn status_shows_last_backup_line() {
+    let v = TestVault::init();
+    let out = v.run(&["status"]);
+    assert!(out.status.success());
+    let stdout = String::from_utf8(out.stdout).unwrap();
+    assert!(stdout.contains("last export:") || stdout.to_lowercase().contains("last export:"),
+            "missing last export line: {stdout}");
+    assert!(stdout.contains("never"), "fresh vault should report 'never': {stdout}");
+}
+
+#[test]
+fn status_shows_recent_backup_after_export() {
+    let v = TestVault::init();
+    let backup_path = v.path().join("v.relbak");
+    v.run_with_backup_pass(
+        &["backup", "export", backup_path.to_str().unwrap()],
+        "test-backup-pass-2026",
+    );
+    let out = v.run(&["status"]);
+    let stdout = String::from_utf8(out.stdout).unwrap();
+    assert!(stdout.contains("last export:") || stdout.to_lowercase().contains("last export:"),
+            "{stdout}");
+    assert!(!stdout.contains("never"), "should NOT say 'never' after export: {stdout}");
+}
+
 #[test]
 fn generate_works_outside_vault() {
     use assert_cmd::cargo::CommandCargoExt;