interrupt: add the passive interrupt core

The library holds only the state its own types need when a Ctrl+C
arrives: the interrupted flag flows check to stand down, the cleanup
hook registry for resources that must not outlive the process (the
ephemeral build chroot), and the live view's reporter slot. The
signal handling itself is CLI wiring and lands separately: nothing
here installs handlers, prints or exits, so a library consumer
embedding these types keeps its own signal disposition.

src/lib.rs

@@ -19,6 +19,9 @@ pub mod deb;
 pub mod debian;
 /// Obtain general information about distribution, series, etc
 pub mod distro_info;
+/// Passive interrupt state: the interrupted flag, the cleanup hook registry
+/// and the live view's reporter slot (the CLI owns the signal handling)
+pub mod interrupt;
 /// Launchpad integration: PPA upload targets and account discovery
 pub mod launchpad;
 /// Lint a source tree: lintian wrapper for full parity plus pkh-native checks (`pkh lint`)