feat: add inline PDF viewer for Custom_PDF objects

Add a /pdf proxy route that forces Content-Disposition inline so PDFs render instead of downloading, and a web viewer that embeds the document in an iframe with a standalone open-in-new-tab link.

apps/web/vite.config.ts

@@ -17,6 +17,7 @@ export default defineConfig({
       '/items': 'http://localhost:3000',
       '/health': 'http://localhost:3000',
       '/asset': 'http://localhost:3000',
+      '/pdf': 'http://localhost:3000',
       '/trace': 'http://localhost:3000',
     },
   },