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/adventure_scheduler.go

@@ -495,6 +495,12 @@ func (p *AdventurePlugin) midnightReset() error {
 		return fmt.Errorf("reset daily actions after 3 attempts: %w", resetErr)
 	}
 
+	// Clear the one-day pet morning-defense buff so it re-rolls fresh each
+	// morning (briefing or overworld DM) instead of leaking permanently.
+	if err := resetAllPetMorningDefense(); err != nil {
+		slog.Error("adventure: failed to reset pet morning defense", "err", err)
+	}
+
 	// Prune expired buffs
 	if err := pruneAdvExpiredBuffs(); err != nil {
 		slog.Error("adventure: failed to prune expired buffs", "err", err)