Add CI workflow and fix CodeQL analysis

[ogajduse]

Summary

• Add dedicated CI workflow with lint (ruff check + format) and test (pytest) jobs
• Tests run across Python 3.11, 3.12, 3.13, 3.14 matrix
• Test job depends on lint passing to save CI minutes on lint failures
• Uses uv for fast dependency installation (matching broker patterns)
• Fix CodeQL workflow: remove duplicate test steps, fix undefined matrix.language bug, upgrade to latest action versions

Test plan

• CI workflow triggers on PR
• Lint job runs ruff check and ruff format --check
• Test job runs pytest across all 4 Python versions
• Test job waits for lint to pass
• CodeQL workflow runs independently

🤖 Generated with Claude Code

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.