refactor(core): [CORE-23] complete keyboard controls and focus lifecycle

packages/artplayer/dist/plugin.ts

@@ -0,0 +1,10 @@
+import type Artplayer from './artplayer'
+
+export type PluginFactory<Host = Artplayer, Result = unknown> = (this: Host, art: Host) => Result
+
+/** Augment this interface with installed plugin results; augmentation does not register a plugin. */
+export interface Plugins {
+  /** Legacy signature: synchronous factories return this registry; Promise factories return a Promise of it. */
+  add: (plugin: PluginFactory) => Promise<Plugins>
+  [name: string]: unknown
+}