feat: add shell auto-completion for bash, zsh, fish, powershell

[Oxygen56]

Adds shell completion support via 'openai completion' subcommand.

What this does

• Adds an openai completion subcommand that generates shell completion scripts for bash, zsh, fish, and PowerShell
• Completion scripts provide context-aware tab completions by calling the CLI itself as a completion source
• Users install by running eval "$(openai completion -s <shell>)" or saving the output to their shell config

Usage

# Bash
eval "$(openai completion -s bash)"

# Zsh
eval "$(openai completion -s zsh)"

# Fish
openai completion -s fish > ~/.config/fish/completions/openai.fish

# PowerShell
openai completion -s powershell | Out-String | Invoke-Expression

Files changed

• src/openai/cli/__init__.py — CLI package entry point
• src/openai/cli/_cli.py — argparse-based CLI with completion subcommand and dynamic completion source handlers
• src/openai/__main__.py — enables python -m openai
• pyproject.toml — adds [project.scripts] entry point for the openai command
• tests/test_cli.py — tests for the completion subcommand

Closes #843

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Remove the bash-completion-only helper call

In vanilla bash environments where the separate bash-completion package has not been loaded (for example a default macOS shell or a minimal container), _init_completion is not defined, so this line returns before the function ever invokes the CLI. The generated setup instructions only ask users to eval "$(openai completion -s bash)", so those users get no bash completions at all unless they happen to have sourced bash-completion separately.

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[chatgpt-codex-connector]

Drop the command name before fish completion lookup

fish documents commandline -opc as the current process tokenized up to the cursor, which includes the command itself. Passing $args unchanged means openai <TAB> calls the helper as openai openai, and _handle_fish_source treats openai as the current word and filters out every top-level completion; this makes fish completions empty at the first argument. The script needs to remove the first token before invoking the Python completion source, as the bash path does with COMP_WORDS[@]:1.

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