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/adventure_pets.go

@@ -206,6 +206,25 @@ func petShouldArrive(pet PetState, house HouseState) bool {
 	return rand.Float64() < 0.30
 }
 
+// maybeRollPetArrivalOnEmerge rolls the pet-arrival check when a player
+// surfaces from an expedition (voluntary extract, abandon, or a survived
+// forced extraction) or revives after death. The arrival roll lives on the
+// emergence seam — not the legacy 08:00 overworld morning DM — because
+// expedition players are almost never in the overworld at the scheduled hour,
+// so the morning roll never reached them. Story beat: while the player was
+// underground, an animal wandered into the empty house looking for food.
+//
+// Safe to call unconditionally on any emergence: petShouldArrive gates on
+// house tier / not-yet-arrived, and petArrivalDM won't clobber an existing
+// pending interaction.
+func (p *AdventurePlugin) maybeRollPetArrivalOnEmerge(userID id.UserID) {
+	pet, _ := loadPetState(userID)
+	house, _ := loadHouseState(userID)
+	if petShouldArrive(pet, house) {
+		p.petArrivalDM(userID)
+	}
+}
+
 // petArrivalDM sends the initial "there's an animal in your house" DM.
 func (p *AdventurePlugin) petArrivalDM(userID id.UserID) {
 	// Don't overwrite an existing pending interaction