fix(scripts): prevent duplicate script attachment per entity

The per-entity script list allowed picking the same script class
twice; the name-keyed runtime silently ignores duplicates, leaving
the extra rows dead weight with unusable enable bits. Enforce
DisallowMultipleComponent semantics: the dropdown of each row only
offers unattached names (own name kept for echo), "+ Add Script"
disables when every registered script is attached, and scene loading
dedupes as a safety net for hand-edited files.

Engine/src/Serialization/SceneSerializer.cpp

@@ -28,6 +28,7 @@
 #include <glm/glm.hpp>
 #include <glm/gtc/quaternion.hpp>
 
+#include <algorithm>
 #include <cmath>
 #include <filesystem>
 #include <fstream>
@@ -672,7 +673,16 @@ namespace Engine::Serialization {
                         ECS::ScriptComponent::Item item;
                         item.name = it["Name"].as<std::string>("");
                         item.active = it["Active"].as<bool>(true);
-                        sc.items.push_back(std::move(item));
+                        // 去重兜底：同名项只收第一份（UI 已杜绝重复，
+                        // 手编场景仍可能写出重复）
+                        const bool dup = std::any_of(
+                            sc.items.begin(), sc.items.end(),
+                            [&](const ECS::ScriptComponent::Item& e) {
+                                return e.name == item.name;
+                            });
+                        if (!dup) {
+                            sc.items.push_back(std::move(item));
+                        }
                     }
                 } else {
                     // 旧格式：Script: {ScriptName: ..., Active: ...}