Implement async manual CSV ingest, unified UI pagination/filters, and serial placeholder strategy

internal/api/helpers.go

@@ -3,6 +3,7 @@ package api
 import (
 	"encoding/json"
 	"io"
+	"log"
 	"net/http"
 	"regexp"
 	"strconv"
@@ -61,7 +62,9 @@ func decodeJSON(r *http.Request, dest any) error {
 func writeJSON(w http.ResponseWriter, status int, payload any) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	_ = json.NewEncoder(w).Encode(payload)
+	if err := json.NewEncoder(w).Encode(payload); err != nil {
+		log.Printf("write json response failed status=%d err=%v", status, err)
+	}
 }
 
 func writeError(w http.ResponseWriter, status int, message string) {