Interrupting the agent while an approval/clarify/sudo/secret prompt is up
left the overlay state dict set with no thread servicing it. The prompt's
worker thread is torn down on interrupt, but read_only (gated on
_command_running) plus the keypress filter kept the CLI input locked until
the prompt's own timeout expired — the terminal appeared frozen.
Drain and clear all four input-blocking overlays on interrupt via a single
helper (_clear_active_overlays_for_interrupt): approval -> deny,
clarify/sudo/secret -> cancel, each guarded so a dead queue can't block the
others; sudo restores the pre-modal draft. Wired into all three interrupt
paths — new-message interrupt, Ctrl+C, and Ctrl+Q. Blocking overlays now
clear AND fall through so one keypress both clears a stale overlay and
interrupts a still-running agent; the /model picker and slash-confirm
foreground prompts keep their cancel-and-return behavior.
Closes#13618.
