Fix remaining flicker and prevent empty page creation on swipe

Flicker: removed View background and super.onDraw() call — canvas is
filled with white explicitly in onDraw before compositing the backing
bitmap, eliminating the clear-then-redraw flash.

Empty page: swiping right on the last page only creates a new page if
the current page has strokes. Empty pages don't spawn more empties.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src/main/kotlin/net/metacircular/engpad/ui/editor/EditorViewModel.kt

@@ -108,11 +108,13 @@ class EditorViewModel(
         if (nextIndex < _pages.value.size) {
             navigateToPage(nextIndex)
         } else {
-            // Add a new page and navigate to it
+            // Only add a new page if the current page has strokes
-            viewModelScope.launch {
+            if (_strokes.value.isNotEmpty()) {
-                pageRepository.addPage(notebookId)
+                viewModelScope.launch {
-                loadPages()
+                    pageRepository.addPage(notebookId)
-                navigateToPage(_pages.value.size - 1)
+                    loadPages()
+                    navigateToPage(_pages.value.size - 1)
+                }
             }
         }
     }

app/src/main/kotlin/net/metacircular/engpad/ui/editor/PadCanvasView.kt

@@ -195,7 +195,11 @@ class PadCanvasView(context: Context) : View(context) {
     }
 
     init {
-        setBackgroundColor(Color.WHITE)
+        // No background — we draw our own white page rect.
+        // This avoids the flicker from View clearing to background color
+        // before onDraw composites the backing bitmap.
+        background = null
+        setWillNotDraw(false)
     }
 
     // --- Public API ---
@@ -235,7 +239,8 @@ class PadCanvasView(context: Context) : View(context) {
     }
 
     override fun onDraw(canvas: Canvas) {
-        super.onDraw(canvas)
+        // Fill entire view with white (no super.onDraw to avoid double-clear flicker)
+        canvas.drawColor(Color.WHITE)
 
         // Draw page background in canonical space
         canvas.withMatrix(viewMatrix) {