fix(ci): restore otf cli to releases

[raspbeguy]

What

Restore the otf client CLI to the release pipeline.

• Add the otf build + archive entries to .goreleaser.yml (darwin + linux, amd64 + arm64), producing the otf_<version>_<os>_<arch>.zip asset.
• Add ./cmd/otf to the Makefile build target.

No Docker image — otf is a downloadable client, not a daemon.

Why

The otf CLI was accidentally dropped from releases in 64716f9 ("fix(ci): broke release process"). That commit migrated goreleaser to v2 and introduced otf-job, but instead of adding a new build entry it repurposed the existing otf build/archive slot:

-  - id: otf
+  - id: otf-job
-    main: ./cmd/otf
+    main: ./cmd/otf-job

As a result, GitHub releases no longer ship the otf binary, even though docs/docs/cli.md still instructs users to download it. There is no documented decision to retire the CLI — it was collateral damage during the otf-job rollout.

Verification

• make build now emits otfd, otf-agent, otf-job, and otf.
• .goreleaser.yml is valid YAML and mirrors the existing otf-job entry (please confirm goreleaser check passes in CI).

[leg100]

Thank you @raspbeguy, merged.