build: run the viewer and the text editor on one engine

Both vendored packages now come from a single build of the engine fork.
The viewer tarball ships without its own copy of pdfium.wasm and loads
the shared engine through EmbedPDF.init({ wasmUrl }), which drops it
from 7.1 MB to 2.1 MB and removes the second WebAssembly instance.

src/js/logic/edit-pdf-page.ts

@@ -8,7 +8,7 @@ import { getEditorDisabledCategories } from '../utils/disabled-tools.js';
 import { editorFontFallback } from '../config/editor-fonts.js';
 
 const embedPdfWasmUrl = new URL(
-  'bentopdf-viewer/dist/pdfium.wasm',
+  'bentopdf-pdfium/editcore.wasm',
   import.meta.url
 ).href;