Resumable, deletion-aware collection and file enumeration (closes #38)

Adds collectionsSince/filesSince taking a starting cursor, returning the resumable max-updationTime cursor and a separate list of tombstoned ids; filesSince throws instead of looping when the server reports hasMore without advancing (closes #7). listCollections/listFiles stay as thin, unaffected wrappers.

Model: opus-4-8

src/index.ts

@@ -1,6 +1,12 @@
 export const VERSION = "0.0.0";
 
-export { Client, type LoginOptions, type ClientSnapshot } from "./client.js";
+export {
+    Client,
+    type LoginOptions,
+    type ClientSnapshot,
+    type CollectionsPage,
+    type FilesPage,
+} from "./client.js";
 export {
     ApiClient,
     ApiError,