Review fixes: align party enemy-HP scaling in the !fight entry path

The P8 diff scaled the enemy's max HP ×1.15 for parties at persist and
per-turn rebuild, but the !fight command's own template stayed unscaled:
the entry banner reported the pre-scale HP, and the opening-round settle
resolved the enemy against the wrong MaxHP ceiling (regen clamp, bloodied
threshold). Mirror the scalar for the banner and align the in-memory
template before the settle. Solo scales by 1.0, so it is untouched.

Also extract enemyActionPlan() so both combat engines share the one
load-bearing action-count computation instead of duplicating it.

Claude-Session: https://claude.ai/code/session_017mEwUmmS7aQTP2NQXj6rUa

internal/plugin/combat_turn_engine.go

@@ -673,11 +673,7 @@ func (te *turnEngine) stepEnemyTurn() {
 	// drawn — so its event stream and RNG draws are unchanged. When the ability
 	// already dealt damage it was the first action, so one fewer follows; for solo
 	// that collapses to the old "the ability stood in for the attack" skip.
-	actions := enemyActionsThisRound(te.st)
-	reuseFirstTarget := !abilityDealtDamage
-	if abilityDealtDamage {
-		actions--
-	}
+	actions, reuseFirstTarget := enemyActionPlan(te.st, abilityDealtDamage)
 	for a := 0; a < actions; a++ {
 		if !(reuseFirstTarget && a == 0) {
 			tgt, alive := te.enemyTarget()