feat(perf): compact strokes (RDP) on persist (R10)

Wires simplifyStroke into the save conversion: a fast Surface-Pen stroke's
hundreds of near-collinear samples are thinned before hitting the DB, shrinking
the row + speeding reload re-rasterization (R10) with no perceptible change. The
live in-memory strokes are untouched — only what we PERSIST is simplified.
Makes the (unit-tested) RDP core load-bearing.

flutter analyze lib/editor clean; 238/238 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/editor/canvas/pen_editor_screen.dart

@@ -11,6 +11,7 @@ import 'package:pdfrx/pdfrx.dart';
 import '../../services/database_service.dart';
 import '../engine/stroke_geometry.dart' show kDefaultPenThinning;
 import '../engine/stroke_model.dart';
+import '../engine/stroke_simplify.dart';
 import '../engine/undo_stack.dart';
 import '../input/diagnostic_logger.dart';
 import '../input/pen_config.dart';
@@ -281,8 +282,13 @@ class _PenEditorScreenState extends State<PenEditorScreen> {
   void _schedulePageSave(int pageIndex, List<PenStroke> strokes) {
     final scheduler = _saveScheduler;
     if (scheduler == null) return;
-    final editorStrokes =
-        strokes.map((s) => EditorStroke.fromPenStroke(s)).toList();
+    // Compact strokes (RDP) before persisting: a fast Surface-Pen stroke lands
+    // hundreds of near-collinear samples; thinning them shrinks the DB row +
+    // speeds reload re-rasterization (R10) with no perceptible change. The live
+    // in-memory strokes are untouched — only what we PERSIST is simplified.
+    final editorStrokes = strokes
+        .map((s) => simplifyStroke(EditorStroke.fromPenStroke(s)))
+        .toList();
     scheduler.schedule(
       'page',
       EditorRepository.pageHostId(_documentId, pageIndex),