feat(blueprint): Add Component nodes + ECS refactor + node-editor fixes (#435)

* 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

* docs: update changeset for auto component registration

* feat(blueprint): add variable nodes (Get/Set Variable)

* docs: update changeset with variable nodes

.changeset/node-editor-collapse-fix.md

@@ -0,0 +1,8 @@
+---
+"@esengine/node-editor": patch
+---
+
+fix(node-editor): 修复节点收缩后连线不显示的问题
+
+- 节点收缩时，连线会连接到节点头部（输入引脚在左侧，输出引脚在右侧）
+- 展开后连线会自动恢复到正确位置