For those who want to explore a bit more:
If you look into the \www\data folder, you’ll find a lot of .json files. These contain game content, and there’s clearly a lot planned for future updates. I suspect a battle system is intended for later versions.
The Level 4 lockpicking set is in there too. You can obtain it with a small amount of manipulation using your save file.
Look for the Items.json file and open it. What you're looking for is on line 11: "id": 9.
Now, Google .rpgsave editor—you should find a website called saveeditonline.
Pick one of your save files from the \www\save folder and back it up first. Then drag and drop your save file onto the website.
It will display the contents of your save, which you can now edit.
Scroll down and click Show data in raw.
All items in your inventory will be displayed like this:
{"1":16.0, "2":17.0, "6":2.0, ... "@c":316.0}, etc.
Insert "9":1.0 in the appropriate place, then scroll down and download the edited version of your save file.
Overwrite your original save file with the edited one.
I’ve tested this with Level 4 doors—some open, some don’t.
You can do the same with other items, weapons, and armor, but they have no use.
Enjoy!