fix: rate limiter memory pruning in Check(), services error leakage replaced with generic messages

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/handlers/services/services.go

@@ -523,7 +523,8 @@ func ServicesEligibleForUserHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if err != nil {
-		http.Error(w, "Failed to get user data: "+err.Error(), http.StatusInternalServerError)
+		log.Printf("Failed to get user data for %s: %v", userID, err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
 		return
 	}
 
@@ -550,7 +551,8 @@ func ServicesEligibleForUserHandler(w http.ResponseWriter, r *http.Request) {
 
 	rows, err := db.Conn.Query(r.Context(), query)
 	if err != nil {
-		http.Error(w, "Failed to fetch services: "+err.Error(), http.StatusInternalServerError)
+		log.Printf("Failed to fetch services: %v", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
 		return
 	}
 	defer rows.Close()