Firstly, at claude.ai you can upload multiple files, so Claude will take those into account and even suggest changes to multiple files. You are then, however, still copy/pasting from a web interface.
Enter cursor (https://www.cursor.com/), you can either use a Claude API key (but it will warn you that all the features they want you to pay for then don't work), or just use the free version, like I am currently. It gets me enough prompts per day to improve my life.
Or you could pay for it, but I have a feeling that this is a sort of WinRAR situation...