Can't use extension's built-in Report function

**Describe the bug**
Attempting to submit a report just returns a 403 error.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to any invalid suggestion
2. Click on 'Report'
3. Fill out the report and hit Submit
4. Nothing appears to happen

**Expected behavior**
Either a notification of the report successfully submitting, or even a notification when there is an error. Instead, nothing happens on the user's side.

**What actually happens**
The call to `https://writewithharper.com/api/problematic-lints` returns a 403 error, "Cross-site POST form submissions are forbidden"

**Platform**
Edge extension on Linux

**Additional context**
Newly installed today, everything should be as up-to-date as possible

Start by reproducing the Report flow in the Edge extension on Linux and inspect the request to https://writewithharper.com/api/problematic-lints. Trace how the extension handles the 403 response and compare it with the endpoint's cross-site POST requirements. Done means reports submit successfully or the user receives a clear error notification.

Written by the indexing model from the issue text.