The multiline editor's key dispatch checked a hardcoded Ctrl/Shift+Enter
-> newline branch before the config-driven tui.input.submit branch, so a
user remap of submit onto Ctrl+Enter was swallowed as a newline and never
submitted. Gate the hardcoded newline fallbacks behind an explicit submit
binding; the bare-LF (iTerm2 Shift+Enter) case stays exempt because its
canonical form is indistinguishable from plain Enter.
Fixes#8906
roboomp
caace28295