<!-- .github/pull_request_template.md -->
## Description
<!-- Provide a clear description of the changes in this PR -->
Description
This PR fix graph visualization access for users with read permissions
(https://github.com/topoteretes/cognee/issues/1182)
- Add permission checks for graph visualization endpoints to ensure
users can only access datasets they have permission to view
- Create get_dataset_with_permissions method to validate user access
before returning a dataset
- Remove redundant dataset existence validation in datasets router and
delegate permission checking to graph data retrieval
- Add comprehensive test suite for graph visualization permissions
covering owner access and permission granting scenarios
- Update get_formatted_graph_data() to use dataset owner's ID for
context
## Testing
Tests can be run with:
```bash
pytest -s cognee/tests/test_graph_visualization_permissions.py
```
## DCO Affirmation
I affirm that all code in every commit of this pull request conforms to
the terms of the Topoteretes Developer Certificate of Origin.
---------
Signed-off-by: EricXiao <taoiaox@gmail.com>
Co-authored-by: Vasilije <8619304+Vasilije1990@users.noreply.github.com>
