fix(library): count trend never played by set total

Nightly snapshot and live trend point use the set total, as stats do.
Newest point now equals stats "never started". Old rows keep old value.
Refs #43

readme.md

@@ -124,7 +124,8 @@ flowchart LR
   moods, the total playtime and moon trips, the drill-down lists) uses the set total, the view
   `user_game_entry_playtime` (V45), the same as the library card, sort and public profile. So do "played", "never
   started" and "under one hour": a set counts once, judged by its set total (also the dashboard "never played" and the
-  oldest unplayed game). Only the nightly trend snapshot `never_played` still uses the counted edition's own minutes.
+  oldest unplayed game) and the trend's never played (`backlog_snapshot`); rows written before #43 keep the old value,
+  they cannot be rebuilt.
   Platforms stay per edition: a Steam + PlayStation set counts on both platforms.
 - **Drill-down**: every countable number opens the games behind it. A `StatKey` (library), `CommunityKey` (landing page)
   or a Pile Points track/bonus row names a number; its SQL "game set" is the same text the number counts, so the