Combat: wire pet procs into the turn-based engine

Pet attacks were never resolved in turn-based fights. Roll the proc once
at fight start (a per-round roll would make a proc near-certain over a
long manual fight), persist it on the session so suspend/resume and
reaper auto-play honor the same outcome, and land a single pet hit on
the player's first acting turn.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/combat_engine.go

@@ -267,6 +267,10 @@ type combatState struct {
 	// the enemy would otherwise attack).
 	enemySkipFirst bool
 
+	// Phase 13 turn-based — pet attack decided once at fight start; the pet
+	// strikes once on the player's first acting turn, which clears this.
+	petProcReady bool
+
 	// Phase 10 SUB2a-ii first-attack one-shots.
 	firstAttackBonusUsed  bool
 	assassinateRerollUsed bool