feat(blueprint): refactor BlueprintComponent as proper ECS Component (#433)

* feat(blueprint): refactor BlueprintComponent as proper ECS Component

- Convert BlueprintComponent from interface to actual ECS Component class
- Add ready-to-use BlueprintSystem that extends EntitySystem
- Remove deprecated legacy APIs (createBlueprintSystem, etc.)
- Update all blueprint documentation (Chinese & English)
- Simplify user API: just add BlueprintSystem and BlueprintComponent

BREAKING CHANGE: BlueprintComponent is now a class extending Component,
not an interface. Use `new BlueprintComponent()` instead of
`createBlueprintComponentData()`.

* chore(blueprint): add changeset for ECS component refactor

* fix(node-editor): fix connections not rendering when node is collapsed

- getPinPosition now returns node header position when pin element is not found
- Added collapsedNodesKey to force re-render connections after collapse/expand
- Input pins connect to left side, output pins to right side of collapsed nodes

* chore(node-editor): add changeset for collapse connection fix

* feat(blueprint): add Add Component nodes for entity-component creation

- Add type-specific Add_ComponentName nodes via ComponentNodeGenerator
- Add generic ECS_AddComponent node for dynamic component creation
- Add ExecutionContext.getComponentClass() for component lookup
- Add registerComponentClass() helper for manual component registration
- Each Add node supports initial property values from @BlueprintProperty

* docs: update changeset with Add Component feature

* feat(blueprint): improve event nodes with Self output and auto-create BeginPlay

- Event Begin Play now outputs Self entity
- Event Tick now outputs Self entity + Delta Seconds
- Event End Play now outputs Self entity
- createEmptyBlueprint() now includes Event Begin Play by default
- Added menuPath to all event nodes for better organization

.changeset/blueprint-ecs-component.md

@@ -0,0 +1,16 @@
+---
+"@esengine/blueprint": minor
+---
+
+feat(blueprint): 添加 Add Component 节点支持 + ECS 模式重构
+
+新功能：
+- 为每个 @BlueprintExpose 组件自动生成 Add_ComponentName 节点
+- Add 节点支持设置初始属性值
+- 添加通用 ECS_AddComponent 节点用于动态添加组件
+- 添加 registerComponentClass() 用于手动注册组件类
+
+重构：
+- BlueprintComponent 使用 @ECSComponent 装饰器注册
+- BlueprintSystem 继承标准 System 基类
+- 简化组件 API，优化 VM 生命周期管理