Add support for uploading file attachments to Grist documents:
- GristClient.upload_attachment() method using multipart/form-data
- upload_attachment tool function with base64 decoding and MIME detection
- Tool registration in server.py
- Comprehensive unit tests (7 new tests)
Returns attachment ID for linking to records via update_records.
Bumps version to 1.3.0.
- Add scripts/test-runner.py with rich progress bars and fail-fast behavior
- Add rich>=13.0.0 as dev dependency
- Update Makefile: `make test` now runs all tests (unit + integration)
- Test runner shows live progress, current test, and summary
Now `make test` runs both unit and integration tests with docker
containers, matching the docker-service-architecture skill guidelines.
Move unit tests from tests/ to tests/unit/ for clearer separation
from integration tests. Update pyproject.toml testpaths and Makefile
test target to reflect the new structure.
