Clean up contact creation and add missing FE fields for last_contacted

frontend/src/App.tsx

@@ -443,6 +443,7 @@ export function App() {
         lon: null,
         last_seen: null,
         on_radio: false,
+        last_contacted: null,
         last_read_at: null,
       };
       setContacts((prev) => [...prev, newContact]);

frontend/src/types.ts

@@ -67,6 +67,7 @@ export interface Contact {
   lon: number | null;
   last_seen: number | null;
   on_radio: boolean;
+  last_contacted: number | null;
   last_read_at: number | null;
 }