claude runtime: interrupting a session kills every process it started

hive-claude 0.1.3 spawns claude as the leader of its own process group,
and its `Cancel::cancel` and idle watchdog signal that group instead of
claude's pid alone. Commands claude started (a `nix build`, a test run)
used to survive a subagent `interrupt` and keep running.

Bump hive-claude to 0.1.3. The subagent `interrupt` call site needs no
code change: `Cancel::cancel(force)` kept its signature.

The harness's `/cancel` and `/logout` did not go through hive-claude:
they ran `kill -INT <pid>` on the claude child they found in /proc. They
now SIGINT the group that child leads, through `libc::kill`. A `claude`
child that leads no group (the `claude plugin` calls) shares the
harness's group and is still signalled alone.

Tests: an interrupted subagent's grandchild dies, for both SIGINT and
`force`, and fails on hive-claude 0.1.2; a harness cancel stops a
turn's grandchild, and fails when only the pid is signalled.

hive-agent/src/web_ui/actions.rs

@@ -69,7 +69,7 @@ pub(super) async fn post_cancel_turn(State(state): State<AppState>) -> Response
             .emit(crate::events::LiveEvent::Note { text: note.into() });
         return (axum::http::StatusCode::OK, "ok").into_response();
     }
-    let out = super::sigint_claude().await;
+    let out = super::sigint_claude();
     let note = match out {
         SigintOutcome::Signalled => {
             // A process actually got signalled — the *next* turn's wake