ci(test): add binary smoke test to verify built artifact runs correctly

[lizhengfeng101]

Description

The test job in ci.yml currently builds the binary to /dev/null:

- name: Build
  run: go build -o /dev/null ./cmd/opencodereview

This only verifies that the code compiles, but does not verify that the resulting binary:

• Starts without panicking (e.g., bad init() functions, missing linked symbols)
• Has correct ldflags injection (--version output)
• Has intact flag registration and dispatch logic (--help output)

Proposed Change

Replace the current Build step and add a Smoke Test step in the existing test job:

- name: Build
  run: go build -o ./opencodereview ./cmd/opencodereview

- name: Smoke test
  run: |
    ./opencodereview --version
    ./opencodereview --version | grep -q "open-code-review"
    ./opencodereview --help
    ./opencodereview --help | grep -q "Commands:"

Why steps in the existing job (not a separate job)?

• The smoke test itself takes <1 second — spinning up a new container just for this is wasteful.
• No artifact passing needed — build and verify in the same job is simplest.
• Semantically it's a natural extension of "Build": compile it, then prove it runs.

Scope

• File: .github/workflows/ci.yml
• Job: test (lines 69–70)
• The cross-compile job should remain unchanged (cross-compiled binaries can't run on the host architecture).

Acceptance Criteria

• test job builds a real binary (not to /dev/null)
• Smoke test verifies --version outputs a string containing open-code-review
• Smoke test verifies --help outputs a string containing Commands:
• CI passes on a PR targeting main

Context

Discovered during a CI gap analysis. The cross-compile job also builds to /dev/null, but that's expected — you can't execute a darwin/arm64 binary on a linux/amd64 runner. The native-platform test job is the right place to verify the binary actually works.

[amh1k]

I would like to take this up @lizhengfeng101