fix: support fish completion script

[Skylvw]

Fixes #41232.

yargs 18 only ships bash/zsh completion templates and its built-in \completion\ command picks the template from , ignoring the shell positional argument — so \opencode completion fish\ emitted a bash/zsh script.

Handle an explicit shell positional ourselves before yargs parses: if \completion\ is called with a known shell (bash/zsh/fish), print the right script and exit. Templates for bash/zsh come from yargs main; fish from yargs' fish template.

Verified: \completion fish|zsh|bash\ each emit the correct script; bare \completion\ falls through to yargs as before. 4 unit tests in packages/opencode/test/cli/completion.test.ts pass.

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found:

• PR fix(cli): honor shell argument in completion command #41235: fix(cli): honor shell argument in completion command - fix(cli): honor shell argument in completion command #41235

This PR appears to address the same issue. Both PRs are focused on handling shell completion scripts properly (bash/zsh/fish) and the current PR #41418 directly references issue #41232 which PR #41235 likely also addresses. The titles suggest they're tackling the same root cause: ensuring the shell argument is properly honored in the completion command.

You should verify if PR #41235 is already merged or if these should be consolidated.

[github-actions]

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

Feel free to open a new pull request that follows our guidelines.