Pets: fire 25% morning event from expedition briefing + fix defense-buff leak

Recovers the genuinely-missing half of ade0335 (orphaned on the unmerged
phase-H-harvest-charges branch). 3ed2e1d redid pet *arrival* via the
emergence seam and explicitly deferred the morning event; this closes
that gap.

- deliverBriefing now rolls the 25% morning pet event (petMorningEvent,
  already present but only wired into the overworld DM that underground
  players never see) and prepends it to the briefing body, granting the
  one-day PetMorningDefense buff.
- Add resetAllPetMorningDefense + wire it into midnightReset. The buff was
  leaking permanently even on HEAD's existing overworld path — it was set
  on the 25% roll but never cleared. Resets the pet_flags_json key in place.

Deliberately omits ade0335's ArrivalPending machinery: arrival is now the
emergence seam's job (3ed2e1d + 978dc5e + 513cf32), so queuing arrival
from the briefing would double-roll it.

internal/plugin/player_meta.go

@@ -909,6 +909,19 @@ func resetAllPlayerMetaDailyActions() error {
 	return err
 }
 
+// resetAllPetMorningDefense clears the one-day pet morning-defense buff for
+// every player. The buff is a fresh morning grant (25% roll in the briefing /
+// overworld DM), so it must not survive past the midnight rollover. The flag
+// lives inside pet_flags_json (see petFlagsJSON), so patch that key in place;
+// only rows where it's currently set are touched.
+func resetAllPetMorningDefense() error {
+	_, err := db.Get().Exec(`
+		UPDATE player_meta
+		   SET pet_flags_json = json_set(pet_flags_json, '$.morning_defense', json('false'))
+		 WHERE json_extract(pet_flags_json, '$.morning_defense') = 1`)
+	return err
+}
+
 // DeathState mirrors player_meta's death-state columns. Phase L5e ports
 // these fields off AdvCharacter (gogobee_legacy_migration.md §7.3 L5e).
 // Mutation surface is large (~50 saveAdvCharacter sites touch death