Fix Docker build: allow pyproject.toml in build context

The .dockerignore was excluding pyproject.toml, which is needed for
`pip install .` to work after the project was modernized to use
pyproject.toml instead of setup.py.

This was causing Docker builds to fail with:
"failed to calculate checksum: /pyproject.toml: not found"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.dockerignore

@@ -74,9 +74,9 @@ test_*.py
 
 # Development files
 requirements-dev.txt
-pyproject.toml
+# pyproject.toml  # NEEDED for pip install - do not exclude!
-setup.py
+# setup.py        # NEEDED for pip install - do not exclude!
-setup.cfg
+# setup.cfg       # NEEDED for pip install - do not exclude!
 
 # Logs and temp files
 *.log