Let a drawing run over as many pages as the note

The ink was stuck on page one while the writing carried on without it,
which stopped making sense the moment a note could run to four pages.
Every page is exported anyway, so every page can be drawn on.

Pages are numbered the way the PDF reader numbers them, and only pages
that carry ink are stored, so the keys are the drawn pages. While drawing
there is always one blank page past the end: pages otherwise come from
how far the writing runs, and to draw on page three you would first have
had to write three pages.

A drawing that lives entirely on page one is still written in the old
single-page shape. Nothing requires that — it means an ordinary note is
stored exactly as it always was, and a device running an older build
still shows it.

The bin clears the page being looked at. Undo and redo work on the
drawing as a whole, because one Undo button that means four different
things depending on where you scrolled is not a button anyone can use.

And a real bug found on the way out: the exporter has written
drawings/<note>.png since the interface was put into English, while the
importer was still looking for zeichnungen/<note>.png. A drawing exported
by this very app came back from its own archive as nothing at all. Both
names are read now, and so are the further pages.

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

frontend/src/App.jsx

@@ -33,7 +33,13 @@ import {
 import { EditorPane } from "./features/notes/EditorPane.jsx";
 import { HistoryModal } from "./features/notes/HistoryModal.jsx";
 import { DrawingLayer } from "./features/drawing/DrawingLayer.jsx";
-import { CANON_W, CANON_H, PREVIEW_DRAWING_W } from "./features/drawing/strokes.js";
+import {
+  CANON_W,
+  CANON_H,
+  PREVIEW_DRAWING_W,
+  drawnSheets,
+  sheetStrokes,
+} from "./features/drawing/strokes.js";
 
 /** Views that are not a notebook and therefore cannot hold a new note. */
 const VIRTUAL_FOLDERS = ["all", "starred", "trash", "dashboard"];
@@ -760,9 +766,12 @@ export default function App() {
             data.setNoteContent(historyFor, content);
             setRestoreEpoch((e) => e + 1);
           }}
-          renderDrawing={(strokes) => (
+          /* The first drawn page stands for the drawing in a thumbnail this
+             small. Asking for page one would show a blank sheet for a note whose
+             ink starts on page three. */
+          renderDrawing={(doc) => (
             <DrawingLayer
-              strokes={strokes.strokes || []}
+              strokes={sheetStrokes(doc, drawnSheets(doc)[0] ?? 1)}
               width={PREVIEW_DRAWING_W}
               height={Math.round((PREVIEW_DRAWING_W * CANON_H) / CANON_W)}
               zIndex={1}