add blueprints

docs/blueprints/04-inventory/34_BPC_KeyItemSystem.md

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+# BPC_KeyItemSystem — Key Item System
+
+**Parent Class:** `ActorComponent`
+**Category:** Inventory
+**Target UE Version:** 5.5–5.7
+**Build Phase:** 3 — Inventory
+
+## 1. Overview
+
+`BPC_KeyItemSystem` manages key items — story-critical objects that unlock doors, trigger narrative events, or are required for puzzle completion. Tracks acquired keys, provides query for door/puzzle unlock checks, and supports key usage notifications.
+
+## 2. Variables
+
+| Variable | Type | Description |
+|----------|------|-------------|
+| `AcquiredKeys` | `TArray<FGameplayTag>` | Tags of all acquired key items |
+| `bShowKeyNotifications` | `bool` | Toast on key pickup |
+| `KeyItemCategory` | `E_ItemCategory` | KeyItem category filter |
+
+## 3. Functions
+
+| Function | Description |
+|----------|-------------|
+| `HasKey` | Checks if player has a specific key by tag |
+| `AddKey` | Registers a key item acquisition |
+| `RemoveKey` | Removes a key (if consumed) |
+| `GetAllKeys` | Returns all acquired key tags |
+| `CanUnlock` | Checks if player meets unlock requirements for a target |
+
+## 4. Event Dispatchers
+
+| Dispatcher | Payload | Description |
+|------------|---------|-------------|
+| `OnKeyAcquired` | `FGameplayTag KeyTag` | New key picked up |
+| `OnKeyUsed` | `FGameplayTag KeyTag`, `AActor* Target` | Key used on target |
+| `OnKeyRemoved` | `FGameplayTag KeyTag` | Key consumed/removed |
+
+## 5. Dependencies
+
+| System | Relationship |
+|--------|--------------|
+| `BPC_InventorySystem` | Keys as inventory items |
+| `BP_DoorActor` | Door unlock queries |
+| `BP_PuzzleDeviceActor` | Puzzle unlock gates |
+| `BPC_NarrativeStateSystem` | Key-based narrative flags |
+
+## 6. Reuse Notes
+- Keys use gameplay tags for generic matching (any key with same tag works)
+- Supports consumable keys (removed after single use) and persistent keys