Rename ship/station scrap drop entities to "debris"

src/lib/ecs/system/DebrisSystem.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <optional>
+#include <vector>
+
+#include <QVector2D>
+
+#include "Tick.h"
+
+#include "entt/entity/entity.hpp"
+
+class EntityAdmin;
+
+// A piece of debris and the scrap amount it still holds (REQ-RES-DEBRIS-DROP).
+struct DebrisInfo
+{
+    entt::entity entity;
+    QVector2D position;
+    int amount;
+};
+
+// Manages debris entities: the salvageable objects dropped by destroyed ships and
+// defence stations (REQ-RES-DEBRIS-DROP). Each piece carries a scrap amount that
+// salvage modules collect one unit at a time (REQ-SHP-SALVAGE).
+class DebrisSystem
+{
+public:
+    explicit DebrisSystem(EntityAdmin& admin);
+
+    entt::entity spawn(QVector2D position, int amount, Tick despawnAt);
+    void         tickDespawn(Tick currentTick);
+
+    // Removes the debris and returns its remaining scrap amount, or nullopt if not found.
+    std::optional<int> consume(entt::entity entity);
+
+    // Collects a single scrap unit from the debris: decrements its amount by one,
+    // destroying the entity once depleted. Returns true if a scrap was collected,
+    // false if the entity is invalid or already empty (REQ-SHP-SALVAGE).
+    bool collectOne(entt::entity entity);
+
+    // Lightweight snapshot for callers that need to iterate all debris.
+    std::vector<DebrisInfo> getAllDebrisInfo() const;
+
+private:
+    EntityAdmin& m_admin;
+};