Replace deprecated schema() with model_json_schema() in mongo_dao.py

[xyf5432]

Summary

embedding_studio/data_access/mongo/mongo_dao.py:127 calls
self.model.schema() in get_model_property_names(). BaseModel.schema() has
been deprecated since pydantic 2.0.0 and emits a PydanticDeprecatedSince20
DeprecationWarning on every call (verified on pydantic 2.13.4).

The project pins pydantic = "2.5.2", so every call to this method emits the
warning.

Impact

• A DeprecationWarning on every call to get_model_property_names(), which
  is invoked for each Mongo collection mapping.
• These methods are scheduled for removal in a future pydantic major release
  (3.0); migrating now avoids a later break.

Suggested fix

Replace .schema() with .model_json_schema(), which returns the same JSON
schema and is available since pydantic 2.0.0:

# before
schema = self.model.schema()
return set(schema["properties"].keys())
# after
schema = self.model.model_json_schema()
return set(schema["properties"].keys())