Read imported PDFs in the app

Stage three: the viewer. Drawing on pages comes next.

pdf.js stays out of the bundle everyone downloads — it is larger than the
rest of the application put together, so it is behind a dynamic import and
a session that never opens a PDF never fetches it. Main bundle grew by
8 kB for the viewer shell; the 162 kB library arrives only when needed.
The worker is bundled rather than pulled from a CDN, because a viewer
that stops working during someone else's outage is not one you can rely
on offline.

Two things that only showed up once it ran in a browser:

- pdf.js 6 calls Uint8Array.prototype.toHex, which only very recent
  browsers have. Anything older failed with "n.toHex is not a function",
  which says nothing about the cause. Now on the legacy build, which
  compiles those away — a little larger, and the difference between
  working everywhere and working on this year's browsers.
- nginx has no MIME type for .mjs and served the worker as
  octet-stream, which a browser refuses to run as a module.

Pages are laid out at their true proportions before anything is drawn, so
the scrollbar is honest immediately and a document mixing portrait and
landscape keeps both — the first version scaled every page to the widest
one, which the suite caught by checking the two aspect ratios differ.

Bytes come from the authenticated attachment route and are cached in
IndexedDB. Content-addressed storage means a cached copy can never be
stale, so a document opened once needs no connection again. Verified with
the network switched off.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/hooks/useNoteData.ts

@@ -33,6 +33,7 @@ export interface NoteData {
   reset: () => void;
 
   createNote: (folderId: string) => Promise<NoteMeta>;
+  importPdf: (folderId: string, file: File) => Promise<NoteMeta>;
   updateNote: (id: string, edit: NoteEdit) => void;
   setNoteContent: (id: string, content: NoteContent) => void;
   toggleStar: (id: string) => Promise<void>;
@@ -185,6 +186,21 @@ export function useNoteData(user: User | null, activeNote: string | null): NoteD
     return note;
   }, []);
 
+  /**
+   * Uploads a PDF and creates the note that holds it.
+   *
+   * Not queued for offline: the file has to reach the server before a note can
+   * point at it, and a note referring to bytes nobody has would be worse than
+   * being told to try again with a connection.
+   */
+  const importPdf = useCallback(async (folderId: string, file: File) => {
+    const attachment = await sync.uploadPdf(file, file.name);
+    const title = file.name.replace(/\.pdf$/i, "") || "Dokument";
+    const note = await sync.createPdfNote(folderId, title, attachment.id);
+    setNotes((p) => [note, ...p]);
+    return note;
+  }, []);
+
   const updateNote = useCallback((id: string, edit: NoteEdit) => {
     if (edit.title !== undefined) {
       const title = edit.title;
@@ -284,6 +300,7 @@ export function useNoteData(user: User | null, activeNote: string | null): NoteD
     reload,
     reset,
     createNote,
+    importPdf,
     updateNote,
     setNoteContent,
     toggleStar,