Add drag-to-reorder pages and fix page navigation from page list

Drag-to-reorder:
- Added sh.calvin.reorderable library for LazyVerticalGrid drag support
- Long-press and drag page thumbnails to reorder
- Page numbers updated in DB on drop
- Visual feedback: slight scale + transparency while dragging

Page navigation fix:
- Clicking a page in "view all pages" now correctly opens that page
  (key(pid) forces EditorScreen recreation with the selected page)

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

app/build.gradle.kts

@@ -68,6 +68,7 @@ dependencies {
     ksp(libs.room.compiler)
 
     implementation(libs.coroutines.android)
+    implementation(libs.reorderable)
 
     testImplementation(libs.junit)
     testImplementation(libs.coroutines.test)