ci: add GitHub Actions workflow for building and testing services

[jdhoffa]

Description

This PR adds a new GitHub Actions workflow that builds and tests all services in the Lucidata system. The workflow builds each service as a separate job and then performs a system test by spinning up all components together.

Changes

• Added .github/workflows/build.yml that:
  • Configures triggers for pushes to main, PRs targeting main, and manual runs
  • Sets up separate build jobs for each service (api, llm_engine, query_runner)
  • Implements a system test job that starts all services together
  • Performs health checks on the running system
  • Ensures graceful shutdown of all components

Implementation Details

• Each build job uses Docker Buildx with GitHub Actions caching for faster builds
• Services are built with appropriate tags to be used in the system test
• The system test includes a 30-second wait period to allow services to initialize
• API health endpoint is checked to verify system functionality
• Cleanup runs in an always step to ensure resources are properly released

Testing

• The workflow has been tested to ensure all services build properly
• System tests verify that the services can run together in an integrated environment

Additional Notes

This implementation provides automated verification that all components can be built and work together, which will help catch integration issues early.

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