feat(play-next): show picks as category rows with reroll per row

Four rows: up next, because you played, longest on list, mood.
Each row rerolls alone and tracks its own loading state.
Mood change reloads only the mood row. Phones scroll each row
sideways; wider screens show 3 columns.

README.md

@@ -28,13 +28,14 @@ To Be Played is split into three repositories:
 - **Coming games**: a game that is not released yet (and nobody played) shows a "Coming <date>" badge in the library, on
   the details page, in the stat game lists and on the public profile. The pile counts only the games Core sends in
   `pileGames`, so coming games are not on it; Core never picks them.
-- **What to play next** (`/play-next`): four backlog picks for a time budget (up to 5 / 15 / 40 h or any) and a mood
-  (story, co-op, chill, action, scary from IGDB; speedrun from speedrun.com). Each pick says why: like a game you
-  played a lot, waiting longest, random, or next in your own backlog order. Reroll without repeats, and "Start playing" in one click.
+- **What to play next** (`/play-next`): four rows of up to 3 backlog games each: up next (your own backlog order),
+  because you played (a similar game for each of your 3 most played), longest on your list, and mood picks. A time
+  budget (up to 5 / 15 / 40 h or any) filters all rows; a mood (story, co-op, chill, action, scary from IGDB; speedrun
+  from speedrun.com) only the mood row. Each row has its own reroll without repeats, and "Start playing" in one click.
+  On a phone each row scrolls sideways.
 - **Backlog order** (`/backlog`, third library tab): all backlog games in your own order. Move a game by drag (pointer
   events, no library, so it works with touch), by the up and down buttons, or "move to top / bottom" in the menu. Each
-  move saves the whole list. The "Up next" dashboard tile shows the first games; the picker has a "next in your
-  backlog" reason.
+  move saves the whole list. The "Up next" dashboard tile shows the first games; the picker's "Up next" row shows the first games.
 - **Your stats** (`/stats`): totals and statuses; the pile in hours, in weeks at your pace of the last 90 days and in
   years of full-time work, and its oldest unplayed game; most played and most loyal games; top genres and moods;
   trips to the moon, the longest gaming day, games started but under one hour; finished games per year; games per platform.