✅(export) add PDF regression tests

To avoid regression issues in PDF export
functionality, this commit introduces end-to-end
tests that compare exported PDFs against
known good reference files.
We compare the PDF on most of the blocks
that the editor supports.
If during a Blocknote release or pull request
there are intentional changes, the reference
files would need to be updated accordingly.
It can be done by uncommenting the line
in the test that saves the newly generated
PDF to the assets folder.

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to
 ### Added
 
 - ✨(backend) add documents/all endpoint with descendants #1553
+- ✅(export) add PDF regression tests #1762
 
 ## [4.3.0] - 2026-01-05