🧪 Add Vitest testing framework with basic composition test

Set up testing infrastructure using Vitest and React Testing Library.
Add test verifying empty MyComposition renders without errors.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

videos/tsconfig.json

@@ -11,5 +11,5 @@
     "forceConsistentCasingInFileNames": true,
     "noUnusedLocals": true
   },
-  "exclude": ["remotion.config.ts"]
+  "exclude": ["remotion.config.ts", "vitest.config.ts"]
 }