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.

packages/http/src/asset.ts

@@ -23,4 +23,9 @@ export function resolveAssetUrl(url: string, baseUrl?: string): string {
 /** Route an external asset URL through the proxy so three.js can load it. */
 export function assetUrl(url: string): string {
   return `/asset?url=${encodeURIComponent(url)}`;
+}
+
+/** Route a PDF URL through the proxy so it renders inline instead of downloading. */
+export function pdfUrl(url: string): string {
+  return `/pdf?url=${encodeURIComponent(url)}`;
 }

packages/http/src/index.ts

@@ -1,3 +1,3 @@
-export { resolveAssetUrl, assetUrl } from './asset.js';
+export { resolveAssetUrl, assetUrl, pdfUrl } from './asset.js';
 export { traceImage } from './trace.js';
 export type { TraceResult } from '@tts/shared';