Update documentation for player, inventory, and weapon systems

- Added C++ status updates for player systems (02-player-systems.md) indicating the implementation status of systems 08-11 and their relation to BPC_StateManager.
- Enhanced inventory systems documentation (04-inventory-systems.md) with C++ status for BPC_InventorySystem and DA_ItemData, clarifying their implementation details.
- Updated weapons systems documentation (08-weapons-systems.md) to reflect the C++ implementation status of BPC_DamageReceptionSystem and stubs for hit reaction and shield defense systems.

docs/developer/08-weapons-systems.md

@@ -2,6 +2,8 @@
 
 **Category Purpose:** These 11 systems form the complete combat layer — weapon actors (ranged and melee), ammo management, combat feedback (hit markers, kill confirm), damage reception and resistance, death cause tracking, firearm specialization, hit reactions, melee combat, recoil patterns, reload mechanics, and shield defense. The `BP_WeaponBase` is the base actor class extended by all weapons; combat flows through `BPC_DamageReceptionSystem` to `BPC_HealthSystem`.
 
+**C++ Status:** System 72 (`BPC_DamageReceptionSystem`) is a full C++ implementation — attach the component directly. Systems 75 (`BPC_HitReactionSystem`) and 79 (`BPC_ShieldDefenseSystem`) are C++ stubs with basic variables and dispatchers — create BP children for full logic. Systems 69-71, 73-74, 76-78 are BP-only.
+
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 ## System Index