HOLD: Use the orka CLI name for Orka 4.0, keep 3.x builds working

[celanthe]

Tracked in DI-753. Orka 4.0 renames the CLI from orka3 to orka, with no alias, and moves its artifacts to the orka/ S3 path (OK-6390). This integration runs the CLI binary directly for deploy, list, delete, config, and token setup.

Changes

• pkg/orka/client.go: all six CLI calls go through one cliBinary = "orka" constant instead of hardcoded "orka3".
• Dockerfile:
  • Picks the path and binary from ORKA_VERSION: orka/…/orka.tar.gz for 4.x and later, orka3/…/orka3.tar.gz for 3.x. Either way, it's installed as /usr/local/bin/orka, with an orka3 symlink for customers' custom scripts. The same source builds images for Orka 3.6 and 4.0.
  • Fixes an existing bug: the CLI download was hardcoded to linux/amd64, so the linux/arm64 image CI publishes has been shipping an x86 CLI. It now downloads the build for TARGETARCH. arm64 Linux builds exist for every 3.x version I checked (3.2.0 through 3.6.3).
  • Default ORKA_VERSION is now 4.0.0 (was 3.1.0).
• .github/workflows/ci.yml: ORKA_VERSION is now 4.0.0 (was 3.2.0).
• README.md and examples/.env: use orka.

Testing

• gofmt and go vet are clean, go build ./... succeeds, and go test ./... passes.
• I ran the new Dockerfile download step against the published 3.6.3 artifacts for amd64 and arm64. Each installs the right architecture (x86-64 and aarch64) as orka, with orka3 linked to it. I didn't do a full multi-arch docker build, because Docker wasn't running locally.
• The 4.x path can't be tested until OK-6390 publishes official/4.0.0/orka/... (currently 403).

Merge and release

• Merge with Orka 4.0 (~Oct 28), after the 4.0 CLI artifacts are public, because the new defaults need them.
• Image tags need a decision. CI tags each release from a single ORKA_VERSION. Orka 3.6 customers need images with a 3.x CLI, so either keep publishing a 3.x line (for example, a build matrix over ORKA_VERSION) or document which image versions pair with which Orka version.

The GitLab and Buildkite changes are in macstadium/orka-integrations#71.

🤖 Generated with Claude Code

[celanthe]

HOLD, pending the OK-6390 decision (targeted Wednesday Oct 14). The orka3 to orka rename is proposed, not decided. As of Oct 9 the CLI still builds as orka3 on releases/cluster/4.0 and master, and no OK-6390 commit exists. Please don't review or merge until the rename is confirmed and lands in code. The release-notes side is held separately in macstadium/macstadium-docs#406.