fix(macos): install passt for podman 5 rootless networking

podman 5 uses pasta as the default rootless network helper; podman 4
used slirp4netns. The spike was written against bookworm's podman 4.3.1,
so its package list never included passt — and the trixie bump (#451)
changed the default out from under it. Every nested container failed to
start with "could not find pasta", while image pulls and the service
itself worked, which disguised a missing dependency as a compat-API bug.

The bootstrap now checks for pasta up front so this fails with a clear
message instead of surfacing at the first `docker run`.

Note the sun_path fix in a12d2191 did NOT cause or cure this; that path
was over the 108-byte limit independently and would have bitten as soon
as attach was reached.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/backend/macos_container/nested-containers-init.sh

@@ -7,7 +7,10 @@ if [ "$uid" -eq 0 ]; then
     exit 1
 fi
 
-for command in podman docker fuse-overlayfs slirp4netns; do
+# pasta is podman 5's default rootless network helper. Checked here so a
+# missing package fails the bootstrap with a clear message rather than
+# letting every later `docker run` die with "could not find pasta".
+for command in podman docker fuse-overlayfs pasta slirp4netns; do
     command -v "$command" >/dev/null 2>&1 || {
         echo "missing nested-container prerequisite: $command" >&2
         exit 1