v0.5.0 — version, update check, completion

[0.5.0] - 2026-06-13

Feature pass. No breaking changes.

Added

• version command (aliases --version / -v) — prints the dctl version,
  which is now also shown in the help header. The version is a constant in
  the script, so it prints instantly with no git or network access.
• Quiet update check — version and self-update do a short-timeout
  git fetch and report how many commits the upstream is ahead. It runs only
  for those two commands, so everyday commands (logs, restart, …) do no
  network I/O. The check stays completely silent on any failure — offline, an
  intranet with no route to GitHub, no git, or not a checkout — so it never
  hangs or adds noise.
• Shell completion (completion.bash, bash + zsh) — completes subcommands,
  global flags, and registered service names (dctl <Tab>, dctl restart <Tab>). install.sh now sources it from your shell rc (idempotent), so it
  activates after the next install.sh run (e.g. via self-update) and a new
  shell.