fix: data-safety fixes from the project review

- autosave: pages a failed flush could not write no longer end up in the
  notebook that is opened next; they go to the recovery folder
- app: finish an open text edit and save before switching notebooks, and
  stay in the notebook when saving fails
- trash: purge by the deletion time in the entry name, not by the folder's
  modification time, which survives the move into .trash
- notebooks are identified by their folder name, so a copied folder is a
  notebook of its own instead of an alias of the original
- manifest: fall back to manifest.json.bak only for a damaged file, not for
  a newer format version or an I/O error
- strokes keep their width after scaling and a restart
- PDF export draws shapes with their stroke width instead of a fixed 1.5 pt
- a first page that fails to load shows the warning; a first page that was
  never saved is an empty page; make-space refuses read-only pages

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

src/i18n/en.rs

@@ -494,6 +494,14 @@ pub const EN: &[(&str, &str)] = &[
     ("🚀 Updates & Versionen", "🚀 Updates & versions"),
     (", PDF-Hintergrund nicht gefunden: {file}", ", PDF background not found: {file}"),
     (", {count} Elemente übersprungen", ", {count} elements skipped"),
+    (
+        "Platz schaffen nicht möglich: Eine der Seiten konnte nicht geladen werden",
+        "Cannot make space: one of the pages could not be loaded",
+    ),
+    (
+        "Nicht gewechselt, Speichern fehlgeschlagen: {err}",
+        "Not switched, saving failed: {err}",
+    ),
     ("Nicht importiert: {err}", "Not imported: {err}"),
     ("Importieren", "Import"),
     ("📄 Importieren", "📄 Import"),