docs: codify entity systems pattern and record combat extensions

docs/SIMULATION_STATE_SCHEMA.md

@@ -26,9 +26,9 @@ simulation. The current world schema is v14 and captures:
 - opportunity records with stable type/status, interested NPC, trigger event,
   target storage/resource/amount, exact later resolution event identity, or a
   deterministic invalidation reason and close tick;
-- a player record holding the player-citizen's hunger, energy, and carried
-  inventory. The player's world position remains presentation-owned and is
-  intentionally not serialized;
+- a player record holding the player-citizen's hunger, energy, health,
+  downed state, and carried inventory. The player's world position remains
+  presentation-owned and is intentionally not serialized;
 - combatant records (health, weapon, faction, position, hostility) for NPC
   defenders and standalone raiders/wolves;
 - faction records (food, warriors, aggression, morale, stance, war plan) for
@@ -248,6 +248,13 @@ to a binary-exact grid and faction food to a binary-exact step so that
 arbitrary world floats round-trip through JSON without breaking deterministic
 continuation checksums.
 
+`PlayerStateRecord` v2 adds `health`, `max_health`, `downed`, and
+`downed_ticks` so wolves and raiders can wound and down the player, with a
+brief forced recovery that restores a fighting baseline. Nested v1 player
+records migrate to full health and standing. The player combatant used by the
+conflict system is derived state and is never serialized; hostile attacks
+reduce the authoritative player health through the ordered event stream.
+
 Current-schema parsing requires unique animal IDs that do not collide with
 resource or storage IDs. An animal reservation must belong to an existing NPC
 whose active feed task targets that exact animal. Every `animal_fed` event