Base CLI's editor UX was better because prompt_toolkit picks the system
editor first, then friendly terminal editors before vi. Do not override
that with a vim-first chain.
Keep the CLI on prompt_toolkit's picker and only set tempfile_suffix='.md'
to avoid the complex-tempfile EEXIST path. Update the TUI resolver to
match prompt_toolkit's fallback order: $VISUAL, $EDITOR, editor, nano,
pico, vi, emacs.
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