Implement git hook for Docker image tagging with git commit hash

[andrewjong]

This PR implements a git hook that automatically updates the DOCKER_IMAGE_TAG in the .env file with the current git commit hash whenever Docker-related files (Dockerfile or docker-compose.yaml) are modified.

Changes:

1. Renamed PROJECT_VERSION to DOCKER_IMAGE_TAG in the .env file
2. Created a pre-commit hook that updates DOCKER_IMAGE_TAG with the git commit hash
3. Updated all docker-compose.yaml files to use the new variable name
4. Added a comment to indicate that the value is auto-generated

This approach eliminates version conflicts between parallel branches by ensuring Docker images are tagged with the exact commit they were built from.

[andrewjong]

John approved on Slack