fix: replace silent json.Encode with error-logging pattern across all handlers

backend/mw/response.go

@@ -2,6 +2,7 @@ package mw
 
 import (
 	"encoding/json"
+	"log"
 	"net/http"
 )
 
@@ -11,7 +12,9 @@ import (
 func RespondJSON(w http.ResponseWriter, status int, data any) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	_ = json.NewEncoder(w).Encode(data)
+	if err := json.NewEncoder(w).Encode(data); err != nil {
+		log.Printf("Failed to encode JSON response: %v", err)
+	}
 }
 
 // RespondError sends a JSON error response with the given status code and message.
@@ -19,6 +22,7 @@ func RespondJSON(w http.ResponseWriter, status int, data any) {
 func RespondError(w http.ResponseWriter, status int, msg string) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	_ = json.NewEncoder(w).Encode(map[string]string{"error": msg})
+	if err := json.NewEncoder(w).Encode(map[string]string{"error": msg}); err != nil {
+		log.Printf("Failed to encode error response: %v", err)
+	}
 }
-