feat(library): hide and unhide games

README.md

@@ -33,6 +33,8 @@ To Be Played is split into three repositories:
   a link to the game's speedrun.com page when it has verified runs, a hint when Steam shows recent playtime for a
   game still in the backlog, and one to set the status to 100 % when
   every achievement is unlocked.
+- **Hide games**: a Steam game (e.g. a playtest or a tool) can be hidden on its detail page. It leaves the lists,
+  the dashboard, the stats and the public profile; the library's "Hidden" filter shows it again for unhiding.
 - **Wishlist** with store price and discount.
 - **Steam account** linked in the settings with "Sign in through Steam": the user signs in on Steam and Auth gets
   the proved Steam ID, never a typed-in one. A Steam ID typed in before shows as "not verified" with a button to