feat(completion): add one-command completion setup

[git-hulk]

Summary

• add clime completion install [shell] for one-command TAB completion setup
• use Cobra completion backend/candidates (generated scripts) and install shell hooks automatically
• support shell autodetection from $SHELL (or explicit arg)
• install behavior:
  • bash/zsh: write script to ~/.clime/completions/clime.<shell> and append profile source hook idempotently
  • fish: write script to ~/.config/fish/completions/clime.fish
  • powershell: return explicit guidance for manual profile setup
• keep existing clime completion <shell> script generation commands unchanged
• add tests for shell normalization/detection and idempotent profile hook updates

Testing

• go test ./...

Closes #12