refactor(web): Extract VirtualScrollManager base class from TimelineManager (#23017)

Extract common virtual scrolling functionality from TimelineManager into
a new abstract VirtualScrollManager base class. This refactoring improves
code organization and enables reuse of virtual scrolling logic.

Changes:
- Create new VirtualScrollManager abstract base class with common virtual
  scrolling state and methods
- Refactor TimelineManager to extend VirtualScrollManager
- Rename 'assetsHeight' to 'bodySectionHeight' for semantic clarity
- Convert methods to use override keyword where appropriate
- Enable noImplicitOverride in tsconfig for better type safety
- Fix ApiError and AbortError class definitions with override keywords

web/src/lib/utils.ts

@@ -60,14 +60,14 @@ interface UploadRequestOptions {
 }
 
 export class AbortError extends Error {
-  name = 'AbortError';
+  override name = 'AbortError';
 }
 
 class ApiError extends Error {
-  name = 'ApiError';
+  override name = 'ApiError';
 
   constructor(
-    public message: string,
+    public override message: string,
     public statusCode: number,
     public details: string,
   ) {