Add bash completion scripts for podman and gh CLI.
Switch bun completion from eval to process substitution
for consistency with other completion scripts.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Source bun's built-in completion output via `bun completions`
(no shell argument needed — it defaults to bash).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>