Fix MongoDB DateTime serialization issues - Replace chrono::DateTime with mongodb::bson::DateTime in models - Update API responses to use timestamp_millis() for JSON serialization - Fix User, Share model DateTime fields - Update all handler responses to return i64 timestamps - This fixes the Kind: invalid type: map, expected RFC 3339 error

backend/src/handlers/health.rs

@@ -9,10 +9,13 @@ pub async fn health_check(State(state): State<AppState>) -> Json<Value> {
         "error"
     };
     
+    // Use timestamp_millis for consistency with other endpoints
+    let timestamp = mongodb::bson::DateTime::now().timestamp_millis();
+    
     Json(json!({
         "status": "ok",
         "database": status,
-        "timestamp": chrono::Utc::now().to_rfc3339()
+        "timestamp": timestamp
     }))
 }