feat: add total? to CursorPaginatedCollectionProp to align with upstream ExO schema [DX-1000]

Add total?: number to CursorPaginatedCollectionProp<T> to match the optional
total field present in the upstream cursor-paginated collection envelope.

The pages optionality change (optional to required) is deferred: making pages
required breaks existing non-ExO consumers that return CollectionProp but are
typed as CursorPaginatedCollectionProp. Needs broader refactor to avoid
breaking create-environment-api.ts and plain-client.ts call sites.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: tylerpina

lib/common-types.ts

@@ -404,6 +404,7 @@ export interface CollectionProp<TObj> {
 
 export interface CursorPaginatedCollectionProp<TObj>
   extends Omit<CollectionProp<TObj>, 'total' | 'skip'> {
+  total?: number
   pages?: {
     next?: string
     prev?: string