Makefile/ko build targets hardcode linux/amd64, breaking arm64 clusters #358

Problem

make deploy and make push only ever produce linux/amd64 images, regardless of the target cluster's architecture:

• deploy-controller/deploy-server invoke ko apply with no --platform flag, and ko's default build platform is linux/amd64 regardless of host OS/arch.
• build-task-runner hardcodes GOOS=linux GOARCH=amd64 for the cross-compile and --platform linux/amd64 for the container build.
• Dockerfile.task-runner hardcodes COPY bin/linux_amd64/ax-task-runner ....

Deploying to an arm64 cluster (e.g. a k3s/Raspberry Pi cluster) with make deploy AX_IMAGE_REPO=... silently builds and pushes amd64 images. Pods then fail with exec format error once they actually pull and try to run.

Fix

I have a fix ready on a branch, but google/ax's pull_request_creation_policy is set to collaborators_only, so I can't open a PR from a fork (github.com/loafoe/ax) — hence this issue instead.

Branch: https://github.com/loafoe/ax/tree/arm64-platform-support
Commit: loafoe@c1d58ba

Summary of the fix:

• Adds KO_PLATFORM (default linux/amd64, unchanged behavior) used as ko apply --platform=$(KO_PLATFORM) in deploy-controller/deploy-server.
• Adds TASK_RUNNER_PLATFORM (default linux/amd64) driving GOARCH, --platform, and a new TASK_RUNNER_GOARCH build-arg passed to Dockerfile.task-runner, which now does COPY bin/linux_${TASK_RUNNER_GOARCH}/ax-task-runner ... instead of a hardcoded amd64 path.
• Verified: make build-task-runner TASK_RUNNER_PLATFORM=linux/arm64 produces a real ELF ... ARM aarch64 binary, and make deploy AX_IMAGE_REPO=... KO_PLATFORM=linux/arm64 was used to successfully deploy ax-controller/ax-server to a live arm64 k3s cluster.

Happy to open a proper PR if I'm added as a collaborator, or if the PR creation policy is relaxed to allow contributions from forks.