refactor: better jwt convert

src/backend/src/main/kotlin/club/itstudio/itmanager/utils/JwtUtils.kt

@@ -103,6 +103,8 @@ class JwtUtils(
         return cal.time
     }
 
-    fun convertToToken(headerToken: String?): String? =
+    fun convertToToken(headerToken: String?): String? {
-        headerToken?.replace("Bearer ", "")
+        val token = headerToken?.replace("Bearer ", "")?.trim()
+        return token?.takeIf { it.isNotEmpty() }
+    }
 }