fix: PDF finger ink, chrome UX, OneNote pens, and pen physics

Wire finger drawing on PDF without breaking pinch; auto-hide page scrubber and fix bounce; share sticky tools with resize and per-page remember; side-button select; separate pen slots with colors; rnote pressure shapes plus tip-velocity width and lower stroke latency.

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

lib/editor/input/pen_config.dart

@@ -19,7 +19,10 @@ enum PenButtonAction {
   toggleTool,
   pan,
 
-  /// Hold to temporarily enable PDF text selection (OneNote-style).
+  /// Rising-edge: switch to the universal stroke [select] tool (OneNote-like).
+  select,
+
+  /// Hold to temporarily enable PDF text selection.
   selectText,
 }
 
@@ -28,7 +31,7 @@ enum PenButtonAction {
 /// Persisted under SharedPreferences key [PenConfigController.prefsKey].
 class PenConfig {
   const PenConfig({
-    this.sideButton = PenButtonAction.eraser,
+    this.sideButton = PenButtonAction.select,
     this.eraserEnd = PenButtonAction.eraser,
     this.pressureGamma = kNaturalPressureGamma,
     this.palmRejectionMs = 150.0,