feat(app): register film and song renderers via plugin system

Create film-renderer.ts and song-renderer.ts as RendererDefinition
plugins using defineAsyncComponent for lazy loading. ContentPanel.vue
now looks up film/song components via getRendererForContentType()
instead of direct imports, enabling future community renderer plugins.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/app/src/plugins/index.ts

@@ -1,4 +1,4 @@
-import { registerPlugin } from '@aiui/core'
+import { registerPlugin, registerRenderer } from '@aiui/core'
 
 export async function initializePlugins(): Promise<void> {
   // Register built-in AI provider
@@ -20,7 +20,14 @@ export async function initializePlugins(): Promise<void> {
     },
   })
 
+  // Register built-in content renderers
+  const { filmRenderer } = await import('./renderers/film-renderer')
+  const { songRenderer } = await import('./renderers/song-renderer')
+  registerRenderer(filmRenderer)
+  registerRenderer(songRenderer)
+
   if (import.meta.env.DEV) {
     console.log('[AIUI] Plugins initialized:', claudeProvider.id)
+    console.log('[AIUI] Renderers registered: film, song')
   }
 }