Implement structured Android entry viewer (#99)

crates/storage/tests/mobile_totp.rs

@@ -145,6 +145,7 @@ fn mobile_totp_catalog_details_and_watch_selection_are_storage_owned() -> TestRe
     let detail = service.detail("otp/alice", 59, &BTreeSet::new(), &mut secrets)?;
     assert_eq!(detail.code().expose(), b"94287082");
     assert_eq!(detail.valid_until(), 60);
+    assert_eq!(detail.remaining_seconds(), 1);
     assert_eq!(detail.period(), 30);
     assert!(!format!("{detail:?}").contains("94287082"));
 
@@ -161,6 +162,7 @@ fn mobile_totp_catalog_details_and_watch_selection_are_storage_owned() -> TestRe
     let detail = service.detail("otp/alice", 60, &selected, &mut secrets)?;
     assert!(detail.shared_with_watch());
     assert_eq!(detail.valid_until(), 90);
+    assert_eq!(detail.remaining_seconds(), 30);
     Ok(())
 }