Pets: roll arrival on expedition emergence, not the 08:00 morning DM

The pet-arrival roll only ran in sendMorningDMs (the 08:00 overworld
morning DM), which is skipped for anyone underground. Expedition players
are almost never in the overworld at 08:00, so the roll never reached
them — the encounter never fired despite the conditions being met.

Move the roll onto the emergence seam via a shared helper
maybeRollPetArrivalOnEmerge, called when a player surfaces alive
(voluntary extract, abandon, survived forced extraction) and on respawn
for underground deaths. Remove the now-dead morning-DM arrival roll.
Story-wise: while the player was out, an animal wandered into the empty
house looking for food.

The 25% morning pet event still rolls only in the overworld DM and has
the same reachability gap; left for a follow-up.

internal/plugin/dnd_expedition_cycle.go

@@ -303,6 +303,14 @@ func (p *AdventurePlugin) deliverBriefing(e *Expedition, now time.Time) error {
 		if err := p.SendDM(uid, body); err != nil {
 			slog.Warn("expedition: send briefing DM", "user", uid, "err", err)
 		}
+		// Emergence seam: a briefing-time forced extraction (starvation /
+		// abyss collapse) surfaces the player alive — roll pet arrival.
+		// Combat/patrol deaths never reach deliverBriefing (the row is
+		// already abandoned), so an abandoned status here means a survived
+		// emergence; those death paths roll on respawn instead.
+		if e.Status == ExpeditionStatusAbandoned {
+			p.maybeRollPetArrivalOnEmerge(uid)
+		}
 	}
 	if err := appendExpeditionLog(e.ID, e.CurrentDay, "briefing",
 		fmt.Sprintf("morning briefing — %.1f SU consumed overnight", burn), line); err != nil {