fix: restore PDF pen capture and overhaul sticky/pens/pages

Reinstall PenCaptureBinding so stylus ink hits again; keep finger Listener translucent under pinch; page-anchor sticky with drag/resize; OneNote pen slots (brush+width+color); blank-note multi-page; default side button to hold-select-text.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/vault_service_test.dart

@@ -237,6 +237,7 @@ void main() {
       expect(loaded, isNotNull);
       expect(loaded!.title, 'My Algebra Notes');
       expect(loaded.docType, 'notebook');
+      expect(loaded.pageCount, 1);
       // The folder holds only the sidecar (and possibly its .bak/.tmp), never
       // an importable source file.
       final files = Directory(expectedFolder)