feat(plugin-sdk): add TypeScript SDK for Infinite Canvas plugins with automatic JSX and build support

plugins/canvas/sdk/src/define-plugin.ts

@@ -0,0 +1,18 @@
+import type { CanvasPlugin, CanvasPluginFactory, PluginRuntime } from "./types";
+
+// 身份帮助函数:为插件对象(或工厂)补全类型,给作者完整补全与校验。
+// 采用 automatic JSX 后,插件通常不再需要 runtime,直接写对象形式即可:
+//
+//   export default definePlugin({ id, name, version, nodes: [...] })
+//
+// 仍支持工厂形式(需要 runtime.version/emit/on 时):
+//
+//   export default definePlugin((runtime) => ({ ... }))
+
+export function definePlugin(plugin: CanvasPlugin): CanvasPlugin;
+export function definePlugin(factory: CanvasPluginFactory): CanvasPluginFactory;
+export function definePlugin(input: CanvasPlugin | CanvasPluginFactory): CanvasPlugin | CanvasPluginFactory {
+    return input;
+}
+
+export type { PluginRuntime };