iris: copy hatch_build.py into Docker images

[rjpower]

• Dockerfile.worker and Dockerfile.controller now COPY hatch_build.py alongside pyproject.toml so the custom hatch build hook (added in Auto-generate protobuf and Connect RPC files via hatch build hook #3631) is present when uv sync runs during the Docker build.
• Without this, the build fails with OSError: Build script does not exist: hatch_build.py.
• Dockerfile.task is unaffected (it doesn't run uv sync at build time, and already has nodejs/npx for proto generation at runtime).

[claude]

Claude finished @rjpower's task in 46s —— View job

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Review

This PR fixes a Docker build break introduced by #3631 (which added a custom hatch build hook). Both Dockerfile.controller and Dockerfile.worker now COPY hatch_build.py alongside pyproject.toml so uv sync can find the build hook. The change is correct and minimal.

• Read changed Dockerfiles and diff
• Verify hatch_build.py exists and is referenced in pyproject.toml
• Confirm Dockerfile.task is unaffected (no uv sync at build time)
• Post review

Findings: None. The fix is straightforward and correct. pyproject.toml declares [tool.hatch.build.hooks.custom] which expects hatch_build.py in the same directory — copying it into the Docker build context is the right fix. Dockerfile.task correctly remains unchanged since it doesn't run uv sync during the build. The layer caching strategy is preserved: hatch_build.py changes rarely, so bundling it with pyproject.toml in the early COPY layer is appropriate.

LGTM.