Bevy should not catch Ctrl+C by default

## Bevy version

0.16 or git

## \[Optional\] Relevant system information

Any Linux (did not test the behavior on Windows).

## What you did

Accidentally write an infinite loop in a system or task.

## What went wrong

Ctrl+C is now completely non-functional and fails to kill the application.

## Additional information

Bevy should not interfere with basic OS functionality like this. No library should ever silently install a Ctrl+C handler by default (but they do it anyways. they always do).

If you absolutely **MUST** do this, the handler should uninstall itself the moment it catches Ctrl+C (from inside the signal handler), so that at least the next attempt will kill the application properly.

This is part of the problem encountered by users in https://github.com/bevyengine/bevy/issues/20355

No file or test is named in the issue. Start by reproducing the infinite-loop case on Linux and tracing where Bevy installs its default Ctrl+C handler; confirm the behavior around repeated interrupts. Done means Ctrl+C retains normal OS termination behavior by default, or the documented opt-in handler no longer prevents a subsequent interrupt from terminating the application.

Written by the indexing model from the issue text.