container: Stop gracefully on podman stop

Containers used `sleep infinity` as PID 1, which never reacts to
SIGTERM: the kernel does not apply default signal dispositions to PID 1,
and sleep has no SIGTERM handler, so every `podman stop` silently
ignored the signal, waited out the full 10-second grace period, and fell
back to SIGKILL.

PID 1 now traps TERM and INT itself and exits on request, so one-off
manual stops of a still-running agent container end immediately instead
of after the kill timeout.

The PID 1 command is baked in at create time, so containers predating
this change are detected and recreated automatically on the next run.

CHANGELOG.md

@@ -1,5 +1,27 @@
 # Release notes
 
+## 1.0.1 — 2026-10-29
+
+`podman stop` now stops a running agent container immediately instead of
+after a 10-second SIGTERM timeout followed by SIGKILL.
+
+### Why
+
+Containers used `sleep infinity` as PID 1. The kernel does not apply
+default signal dispositions to PID 1, and `sleep` has no SIGTERM handler,
+so the stop signal was silently ignored and every stop fell through to
+SIGKILL. PID 1 now traps TERM (and INT) itself and exits on request:
+
+```sh
+trap "exit 0" TERM INT; sleep infinity & wait
+```
+
+### Upgrading
+
+The PID 1 command is baked in when a container is created, so existing
+containers are detected on the next run and recreated automatically.
+Nothing in the container home is touched.
+
 ## 1.0.0 — 2026-10-29
 
 Containers now run with rootless Podman instead of Docker.