fix(canvas): compact page pill + pen diagnostic

Page slider is no longer persistent: a compact prev/'n/total'/next pill;
tapping the label reveals the slider (collapses again), so it stops
blocking the page. Add a pen-pressure diagnostic toggle (bug icon) that
shows the live kind/pressure/min/max Windows delivers — to pin down why
pressure reads flat on the Surface Pen.

lib/editor/canvas/pen_canvas.dart

@@ -42,8 +42,14 @@ class PenCanvas extends StatefulWidget {
     this.allowFingerDrawing = false,
     this.minScale = 0.5,
     this.maxScale = 8.0,
+    this.onPenDebug,
   });
 
+  /// Debug hook: called with a readout of the latest pen event
+  /// (kind / pressure / pressureMin / pressureMax) so we can see what Windows
+  /// actually delivers. Null in release UI.
+  final void Function(String readout)? onPenDebug;
+
   /// The rendered PDF page bitmap, already sized to [pageSize].
   final Widget pageWidget;
 
@@ -249,8 +255,18 @@ class _PenCanvasState extends State<PenCanvas> {
 
   // --- Listener callbacks ---------------------------------------------------
 
+  void _emitPenDebug(PointerEvent event) {
+    final cb = widget.onPenDebug;
+    if (cb == null) return;
+    cb('${event.kind.name}  p=${event.pressure.toStringAsFixed(3)}  '
+        'min=${event.pressureMin.toStringAsFixed(2)} '
+        'max=${event.pressureMax.toStringAsFixed(2)}  '
+        'tilt=${event.tilt.toStringAsFixed(2)}');
+  }
+
   void _onPointerHover(PointerHoverEvent event) {
     if (_isStylus(event.kind)) {
+      _emitPenDebug(event);
       // Detect eraser (barrel button / inverted) while hovering.
       _eraserActive = _isEraserSignal(event);
     }
@@ -258,6 +274,7 @@ class _PenCanvasState extends State<PenCanvas> {
 
   void _onPointerDown(PointerDownEvent event) {
     if (event.kind == PointerDeviceKind.trackpad) return;
+    if (_isStylus(event.kind)) _emitPenDebug(event);
 
     _activePointers[event.pointer] = event.kind;
 
@@ -282,6 +299,7 @@ class _PenCanvasState extends State<PenCanvas> {
   }
 
   void _onPointerMove(PointerMoveEvent event) {
+    if (_isStylus(event.kind)) _emitPenDebug(event);
     if (event.pointer != _drawPointer) return;
     if (_activePointers.length >= 2) return; // pinch owns it
     _extendStroke(event);