♻️(back) replace Ypy by pycrdt

Ypy is deprecated and unmaintained. We have problem with parsing
existing documents. We replace it by pycrdt, library actively maintained
and without the issues we have with Ypy.

src/backend/pyproject.toml

@@ -47,18 +47,19 @@ dependencies = [
     "factory_boy==3.3.3",
     "gunicorn==23.0.0",
     "jsonschema==4.23.0",
+    "lxml==5.3.1",
     "markdown==3.7",
     "mozilla-django-oidc==4.0.1",
     "nested-multipart-parser==1.5.0",
     "openai==1.68.2",
     "psycopg[binary]==3.2.6",
+    "pycrdt==0.12.10", 
     "PyJWT==2.10.1",
     "python-magic==0.4.27",
     "requests==2.32.3",
     "sentry-sdk==2.24.0",
     "url-normalize==1.4.3",
     "whitenoise==6.9.0",
-    "y-py==0.6.2",
 ]
 
 [project.urls]