413 Request Entity Too Large on import - no UI warning + possible to bypass

[msub2]

Describe the bug
A user recently reported to me that they received a 413 - Request Entity Too Large error when attempting to import a file larger than 2MB. While I don't have the exact file they used, I was able to replicate the behavior by attempting to upload a shortcut file that pointed to a larger exe. This was not caught by the size checker. Additionally, when directly choosing a file over the size limit there is no visual indicator other than the import button being disabled, although I can see in code that there is supposed to be.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://books.theunseen.city/import
2. Click on Browse
3. Select a file over 2 MB large.
4. See that there is no visual feedback other than the disabled import button.

OR

3. Select a shortcut to a file over 2 MB large.
4. Receive a 413 error on submit

Expected behavior
User should be shown clear feedback that the file they have selected is too large.

Screenshots
If applicable, add screenshots to help explain your problem.

Instance
https://books.theunseen.city/

Additional context
The primary issue for the user here is moreso that they need a higher file size limit to import their data, the lack of warnings is essentially a secondary issue I noticed when checking myself.

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Desktop (please complete the following information):
- OS: Windows 10
- Browser: Firefox
- Version: 106

[msub2]

The bypass issue could probably be solved just by restricting the filepicker to .csv files, since those are the only kinds listed as being valid for import.

[mouse-reeve]

TSV is also a valid format, but you're right that it ought to check