Fix edge swipe and page list navigation

Edge swipe:
- Only detect from RIGHT edge (swipe left = next page)
- Left edge no longer triggers page nav (avoids conflict with system
  back gesture)
- Previous page navigation via binder dropdown or system back only

Page list navigation:
- Simplified selectedPageId handling — read and clear synchronously
  during recomposition instead of async StateFlow observation
- Fixes issue where clicking a page in view-all-pages went to last
  visited page instead of the selected one

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

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

@@ -85,8 +85,8 @@ fun EditorScreen(
         }
         canvasView.onEdgeSwipe = { direction ->
             when (direction) {
-                PadCanvasView.SwipeDirection.LEFT -> viewModel.navigateNext()
-                PadCanvasView.SwipeDirection.RIGHT -> viewModel.navigatePrev()
+                PadCanvasView.SwipeDirection.NEXT -> viewModel.navigateNext()
+                PadCanvasView.SwipeDirection.PREV -> viewModel.navigatePrev()
             }
         }
         viewModel.onStrokeAdded = { stroke ->

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

@@ -110,7 +110,10 @@ class PadCanvasView(context: Context) : View(context) {
     private var moveOriginX = 0f
     private var moveOriginY = 0f
 
-    enum class SwipeDirection { LEFT, RIGHT }
+    enum class SwipeDirection {
+        NEXT,  // Swipe from right edge toward left = next page
+        PREV,  // Swipe from left edge toward right = prev page
+    }
 
     // --- Zoom/pan state ---
     private var zoom = 1f
@@ -793,7 +796,7 @@ class PadCanvasView(context: Context) : View(context) {
                 fingerDownY = event.y
                 // Detect if finger started at screen edge
                 val edgeZone = width * EDGE_ZONE_FRACTION
-                isEdgeSwipe = event.x < edgeZone || event.x > width - edgeZone
+                isEdgeSwipe = event.x > width - edgeZone // Only right edge for next page
             }
             MotionEvent.ACTION_MOVE -> {
                 if (!scaleGestureDetector.isInProgress && event.pointerCount == 1) {
@@ -818,13 +821,9 @@ class PadCanvasView(context: Context) : View(context) {
                     val dy = event.y - fingerDownY
                     val absDx = Math.abs(dx)
                     val absDy = Math.abs(dy)
-                    if (absDx > EDGE_SWIPE_MIN_PX && absDx > absDy * 2) {
-                        // Horizontal swipe detected
-                        if (dx < 0) {
-                            onEdgeSwipe?.invoke(SwipeDirection.LEFT)
-                        } else {
-                            onEdgeSwipe?.invoke(SwipeDirection.RIGHT)
-                        }
+                    if (absDx > EDGE_SWIPE_MIN_PX && absDx > absDy * 2 && dx < 0) {
+                        // Swipe left from right edge = next page
+                        onEdgeSwipe?.invoke(SwipeDirection.NEXT)
                     }
                 }
                 isEdgeSwipe = false

app/src/main/kotlin/net/metacircular/engpad/ui/navigation/NavGraph.kt

@@ -2,7 +2,6 @@ package net.metacircular.engpad.ui.navigation
 
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
-import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.key
 import androidx.compose.runtime.mutableStateOf
@@ -92,15 +91,12 @@ fun EngPadNavGraph(
                 }
             }
 
-            // Observe page selection from the page list screen
+            // Check for page selection from the page list screen
             val savedState = backStackEntry.savedStateHandle
-            val selectedPageId by savedState.getStateFlow("selectedPageId", 0L)
-                .collectAsState()
-            LaunchedEffect(selectedPageId) {
-                if (selectedPageId > 0) {
+            val selectedPageId = savedState.get<Long>("selectedPageId")
+            if (selectedPageId != null && selectedPageId > 0) {
                 initialPageId = selectedPageId
-                    savedState["selectedPageId"] = 0L
-                }
+                savedState.remove<Long>("selectedPageId")
             }
 
             val ps = pageSize