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_extract.go

@@ -179,7 +179,13 @@ func (p *AdventurePlugin) handleExtractCmd(ctx MessageContext, _ string) error {
 	}
 	b.WriteString(fmt.Sprintf("Loot, XP, and coins are kept. The dungeon stays where you left it — `!resume` within 7 days to come back. After %s the expedition expires.",
 		(time.Now().UTC().Add(extractResumeWindow)).Format("2006-01-02 15:04 MST")))
-	return p.SendDM(ctx.Sender, b.String())
+	if err := p.SendDM(ctx.Sender, b.String()); err != nil {
+		return err
+	}
+	// Emergence seam: surfacing from a run is when an animal may have moved
+	// into the empty house.
+	p.maybeRollPetArrivalOnEmerge(ctx.Sender)
+	return nil
 }
 
 // ── !resume command ─────────────────────────────────────────────────────────