Update DevExpress migration docs and plan

Added `ZoomLevelChanged` to available events in `DEVEXPRESS_V25_LIMITATIONS.md` and clarified missing events. Created a detailed migration plan in `MIGRATION_PLAN.md` for transitioning from PDF.js to DevExpress DxPdfViewer v25.2.3, including a hybrid approach, testing checklist, and rollback plan. Summarized research findings and API verification in `SESSION_SUMMARY.md`, highlighting limitations, risks, and recommendations for the migration.

DEVEXPRESS_V25_LIMITATIONS.md

@@ -20,10 +20,14 @@
 
 ---
 
+## Available Events
+
+- **`CustomizeToolbar`** – Allows toolbar customization
+- **`ZoomLevelChanged`** – Fires when ZoomLevel property changes (EventCallback<double>)
+
 ## Missing Events (NOT AVAILABLE in v25.2.3)
 
-- **`PageNumberChanged`** – Not available
-- **`ZoomLevelChanged`** – Not available
+- **`PageNumberChanged`** / **`ActivePageIndexChanged`** – Not available
 - User scrolling or native toolbar page changes do not trigger C# code
 
 ---
@@ -43,12 +47,6 @@
 
 ---
 
-## Available Event
-
-- **`CustomizeToolbar`** – Only available event for toolbar customization
-
----
-
 ## Critical Integration Notes
 
 ### ZoomLevel takes factor, not percentage
@@ -230,4 +228,4 @@ protected override async Task OnAfterRenderAsync(bool firstRender)
 
 - DevExpress official documentation: https://docs.devexpress.com/Blazor/DevExpress.Blazor.PdfViewer.DxPdfViewer
 - Verified package: `DevExpress.Blazor.PdfViewer` v25.2.3
-- **Note:** AI-suggested APIs (GoToPageAsync, PageNumberChanged, ZoomLevelChanged, ZoomAsync, ToolbarVisible) are NOT real. Do not use.
+- **Note:** AI-suggested APIs (GoToPageAsync, PageNumberChanged, ActivePageIndexChanged, ZoomAsync, ToolbarVisible) are NOT real. Do not use.