feat(inbox): add expandable details to digest notes

Digest notes only showed counts. Now a digest note opens to list its
games and items, grouped by kind. The list loads once, from
GET /api/inbox/{id}/details. Achievements show 5 per game first.

README.md

@@ -177,7 +177,9 @@ flowchart LR
   settings page lists who you follow ("Unfollow") and who follows you ("Remove", a private follower shows as "Private
   user"). Core writes one inbox note per followed user and batch (new games, achievements, status changes, wishlist
   adds; what the profile hides is left out). `/inbox` (bell in the header, with the unread count) lists the newest 50 notes
-  and marks them read; a user who goes private ends the follow with a note. Two more notes come from the user's own
+  and marks them read; a digest note opens inline (click) and lists its games, achievements, status changes and wishlist
+  items, while you still follow the person and the part is public (5 achievements per game, then "show all"); a user
+  who goes private ends the follow with a note. Two more notes come from the user's own
   PlayStation link (`PSN_EXPIRING` about 2 days before it ends, `PSN_EXPIRED` when it has ended), with a link to the
   settings. Notes older than 90 days are deleted.
 - **What's new**: a dialog on the dashboard shows the news entries the user has not seen yet, newest first. "Got it"