fix(cli): add trailing newline to --help output

[MuoDoo]

Issue for this PR

Closes #22115

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Running opencode --help outputs help text without a trailing newline, causing the shell prompt to appear on the same line as the last line of output.

The show() function in packages/opencode/src/index.ts writes to stderr via process.stderr.write(), but yargs help output doesn't include a trailing newline. Both code paths (with and without the logo) now check for and append EOL when missing.

How did you verify your code works?

Ran opencode --help 2>&1 | xxd | tail -5 before and after the fix:

• Before: output ends with [string] (hex 5d), no 0a newline
• After: output ends with 0a (newline)

Screenshots / recordings

N/A — CLI output change, not UI.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR