Implement the 013-hp-status-indicators feature that adds visual HP status indicators to combatant rows with a pure domain function deriving bloodied/unconscious states

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/domain/src/hp-status.ts

@@ -0,0 +1,11 @@
+export type HpStatus = "healthy" | "bloodied" | "unconscious";
+
+export function deriveHpStatus(
+	currentHp: number | undefined,
+	maxHp: number | undefined,
+): HpStatus | undefined {
+	if (currentHp === undefined || maxHp === undefined) return undefined;
+	if (currentHp <= 0) return "unconscious";
+	if (currentHp < maxHp / 2) return "bloodied";
+	return "healthy";
+}