Fix #58: mapValidated on MultipleChoice prompts and move error display to bottom

[kevin-lee]

Fix #58: mapValidated on MultipleChoice prompts and move error display to bottom

Bug:

cue4s-multiple-choice-bug.mp4

Why was the error moved to the bottom?

After the first fix, the list rendering was fine, but it had another issue. Please watch this video.

cue4s-multiple-choice-bug-fixed-but-another-bug.mp4

The error message at the bottom (SOLUTION IN THIS PR)

This is a demo of the fix that this PR offers.

cue4s-multiple-choice-bug-fixed-all.mp4

Two bugs existed in PromptFramework.mapValidated when used with MultipleChoice prompts:

1. After a validation rejection showed an error message, subsequent non-ENTER
   actions (TAB toggle, arrow keys) did not clear the error. The inner
   framework's status was permanently stuck at Running(Left(err)) because
   non-ENTER handlers use identity for status, causing stale error rendering
   and visual artifacts (duplicate/shifted items on terminal).

2. After a first rejection, selecting then deselecting and pressing ENTER again
   produced no visible feedback because the rendering was already identical to
   the displayed error state.

Fix in PromptFramework.mapValidated (two coordinated changes):

• renderState: translate the outer wrapper's Running(Left(err)) status
  directly into an inner self.Status.Running(Left(err)) for rendering,
  instead of always reading self.currentStatus() which could be stale.

• handleEvent: backward-propagate self.Status.Init instead of
  self.Status.Running(Left(err)), guarded by innerWasFinished to only
  apply when the inner was actually Finished (not when it was Running
  with its own validation error, e.g. InteractiveTextInput).

Fix in InteractiveMultipleChoice.renderState:

• Move the error message rendering from between instructions and options to
  after the options list. When no error is present, a blank line is rendered
  in its place. This keeps the line count constant across error/non-error
  states, preventing terminal scroll-induced cursor offset issues that caused
  duplicate rendering when the prompt was near the terminal bottom.

Also adds a validated-multi interactive example for manual testing.