Capture and publish commit hash in Docker image and ROS topic

[Copilot]

• Modify Dockerfile to capture commit hash as build arg and environment variable
• Update arm_base.py to publish commit hash to /config/commit topic at startup
• Update GitHub Actions workflow to pass commit hash during build
• Update README with build instructions including commit hash
• Test the changes to ensure they work correctly
• Simplify commit hash publishing to one-liner per review feedback
• Move COMMIT_HASH to end of Dockerfile to preserve Docker cache

Implementation Summary

The commit hash is now captured at Docker build time and published to /config/commit as a ROS String topic at startup.

How it works:

1. Docker build accepts COMMIT_HASH as a build argument (defaults to "unknown")
2. The commit hash is baked into the image as an environment variable (at the very end to preserve cache)
3. ArmBase class publishes to /config/commit topic (latched) at startup in a single line
4. Users can read the commit with rostopic echo /config/commit

Changes:

• Dockerfile: Added ARG and ENV for COMMIT_HASH at the end to avoid cache invalidation
• arm_base.py: One-liner publisher for /config/commit topic
• GitHub workflow: Passes github.sha as build-arg
• README: Updated build command with commit hash

All tests pass successfully!

Original prompt

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This section details on the original issue you should resolve

<issue_title>Capture the commit hash</issue_title>
<issue_description>1. The Docker build should bake the environment variable COMMIT_HASH into the image.

As a hack for now:

2. The arm base class should publish /config/commit as a string containing COMMIT_HASH or "unknown" once at startup.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #95

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[rgov]

@copilot This will invalidate the Docker cache on every commit—no bueno. Please move this to the very end of the Dockerfile.

Why are you kinda bad?

[Copilot]

@copilot This will invalidate the Docker cache on every commit—no bueno. Please move this to the very end of the Dockerfile.

Why are you kinda bad?

Moved COMMIT_HASH ARG and ENV to the end of the Dockerfile to preserve Docker cache. (commit: 1e8a6d5)

[figuernd]

I think moving commit publication to web node (or utilizing the environment variable publishing mechanism there) would make more sense for code related to header files/provenance.

[figuernd]

I wonder if there's somewhere more appropriate than arm_base.py. If the purpose of this is primarily to put it in the web_node for provenance, it does already support pulling environment variables (though I'm not sure how well it works):

PhytO-ARM/src/phyto_arm/src/web_node.py

Line 53 in edb93e3

response_values[name] = os.environ[var_name]

[rgov]

I think this is only captured in the bin files but not the ROS bags.

I agree there's no obvious place to put this. We could just run rostopic echo once at startup or something, but currently when the node finishes it will tear down everything.