feat(common): PendingStatus wire type + Default impl on PendingFlag

PendingStatus carries an explicit 'present' bool next to a PendingFlag
because zvariant doesn't support Option<T>. Two new serde tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

common/src/types.rs

@@ -36,7 +36,7 @@ pub struct Credential {
     pub created_unix: u64,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, zvariant::Type)]
+#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize, zvariant::Type)]
 pub struct PendingFlag {
     pub required_methods: Vec<Method>,
     pub created_unix: u64,
@@ -46,6 +46,13 @@ pub struct PendingFlag {
     pub re_enroll: bool,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, zvariant::Type)]
+pub struct PendingStatus {
+    pub present: bool,
+    /// Contents are the default when `!present`; consumer must check `present` first.
+    pub flag: PendingFlag,
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, zvariant::Type)]
 pub struct Violation {
     pub user: String,
@@ -119,4 +126,30 @@ mod tests {
         let back: Credential = serde_json::from_str(&json).unwrap();
         assert_eq!(c, back);
     }
+
+    #[test]
+    fn pending_status_serde() {
+        let s = PendingStatus {
+            present: true,
+            flag: PendingFlag {
+                required_methods: vec![Method::Fido2],
+                created_unix: 1_700_000_000,
+                deadline_unix: 0,
+                re_enroll: false,
+            },
+        };
+        let bytes = serde_json::to_vec(&s).unwrap();
+        let back: PendingStatus = serde_json::from_slice(&bytes).unwrap();
+        assert_eq!(s, back);
+    }
+
+    #[test]
+    fn pending_status_default_when_absent() {
+        let s = PendingStatus {
+            present: false,
+            flag: PendingFlag::default(),
+        };
+        assert!(!s.present);
+        assert!(s.flag.required_methods.is_empty());
+    }
 }