fix(gui,cli): count what a folder's first scan has checked (#46)

The first pass over a synced folder has no baseline to estimate from, so
its scan showed only "checking for changes…" in the app and "scanning…"
in `pdfs sync list`. For a large folder that scan reads every item on
Proton Drive before anything downloads, which takes many minutes and
looked stuck. Both now show how many items the scan has checked so far.

docs/CHANGELOG.md

@@ -59,6 +59,11 @@ scratch (user data in `staging/` and `recovery/` is never touched by this).
   files again instead, sync the folder from scratch. Restoring folders also logs why it
   skipped a folder.
 
+- **The first sync of a folder shows how far its scan got** (#46). Before anything downloads,
+  the first pass reads every item on Proton Drive, which takes many minutes for a large folder.
+  The folder showed only "checking for changes…" all that time, and `pdfs sync list` only
+  `scanning…`, which looked stuck. Both now count the items checked so far.
+
 - **Saved public links show the name of what they point at**, in the app and in `pdfs bookmarks`,
   instead of "Shared link". For a link with a custom password, the address no longer has the custom
   password stuck to its end, so it matches the link the web shows and the page asks for the