Standardize --version output to include Go runtime and target platform

[Copilot]

This updates --version to emit a single standardized string: projectName version vX.Y.Z (goX.Y, os/arch). The current output omitted compiler/runtime and platform details, which are now included for consistent release/runtime identification.

• Version output contract

  • Switched from Version: <value> to a canonical format:
    • clip4llm version <normalized-version> (<go-version>, <goos>/<goarch>)
  • Ensures the v prefix is present in version output when missing.

• Implementation

  • Added a small formatter helper (formatVersionOutput) and routed --version through it.
  • Uses runtime metadata from Go stdlib (runtime.Version(), runtime.GOOS, runtime.GOARCH).

• Coverage

  • Added focused unit tests for:
    • version normalization (1.2.3 -> v1.2.3)
    • preserving already-prefixed versions (v2.3.4).

func formatVersionOutput(projectName, version string) string {
	if version != "" && !strings.HasPrefix(version, "v") {
		version = "v" + version
	}
	return fmt.Sprintf("%s version %s (%s, %s/%s)",
		projectName, version, runtime.Version(), runtime.GOOS, runtime.GOARCH)
}