Bare PDMODE / PDSIZE / LTSCALE / CELTSCALE now enter a generic
ValuePromptCommand front-end that prompts for the value and delegates to the
existing inline `<name> <value>` handler via CmdResult::Dispatch, so they
prompt step-by-step like UCS. A bare Enter reports the current value;
`PDMODE 3` still works as one typed / headless line.
Only pure single-value setting commands are converted. Dialog-opening
commands (LAYER, PURGE, DIMSTYLE, STYLE …) intentionally keep their
bare-name behaviour (open the panel), and subcommand-tree commands keep
their inline handlers — all already typable with arguments since F1.
Adds headless test value_prompt_commands_inline_args. Fourth phase of the
unified step driver.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>