Keep the right prompt out of the committed prompt frame

[tleonhardt]

Problem

With enable_rprompt=True, the right prompt was redrawn beside every accepted command line in the scrollback, not just on the live prompt line:

myapp> echo one                            cwd=/Users/you/src/cmd2
one
myapp> echo two                            cwd=/Users/you/src/cmd2
two

Cause

prompt-toolkit ends every Application.run() with a final render, and that frame is what stays on the terminal. PromptSession filters its bottom toolbar container with ~is_done so the toolbar is excluded from it, but the right prompt is a plain Float with no such filter (shortcuts/prompt.py:157-162), so it is drawn into the committed frame once per command.

Fix

Wrap that float in a ConditionalContainer with the same ~is_done filter the toolbar already gets.

The float is located by its "class:rprompt" style rather than by its private _RPrompt type, matching how cmd2 already identifies the toolbar container by "class:bottom-toolbar". A layout that does not contain it is left alone — the right prompt is cosmetic, and an upstream layout change must not stop the application from starting.

main_session.rprompt is untouched, so main_session.rprompt == get_rprompt still holds and the existing test_enable_rprompt passes unchanged.

Verification

Driving examples/getting_started.py through a real pty:

	accepted command lines	...that also carry the right prompt
main	3	3
this branch	3	0

tests/test_cmd2.py::test_rprompt_is_not_drawn_into_the_committed_line asserts the right prompt is not rendered while is_done. Making the fix a no-op fails it with the right prompt was drawn into the committed final frame.

• make check clean (ruff, prettier, typos, ty, mypy --strict)
• make test: 1857 passed, 2 skipped
• make docs-test clean

Provenance

Found while investigating the bottom toolbar flicker on #1748. That branch fixed this incidentally as a side effect of a much larger architecture change which does not fix the flicker and should not be merged; this extracts the one confirmed win as a standalone change against main.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.64%. Comparing base (c11a55f) to head (78f3a1f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1749   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files          23       23           
  Lines        5960     5973   +13     
=======================================
+ Hits         5939     5952   +13     
  Misses         21       21           

Flag	Coverage Δ
unittests	99.64% <100.00%> (+<0.01%)	⬆️

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