docs: the board's not-started toggle, and why it ships off

F1 said the timeline plots what the reader can see, which is now half
true, and the prefs key space did not list the field the board writes.
Both record the argument the code only implies: the window is drawn from
what is plotted, so on-by-default is not a fuller board, it is a smaller
one for everything that is actually running.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/DATA-MODEL.md

@@ -218,7 +218,8 @@ Namespaced, versioned, and small. Nothing here ever goes to the server.
 "gacha-tracker:v1:daily"        // { [id]: { days: ["2026-08-15", ...], at } }
 "gacha-tracker:v1:ignored"      // { [eventId]: { at } }  — "stop showing me this"
 "gacha-tracker:v1:prefs"        // { region, hiddenGames[], knownGames[]?, focusGame, sort, view,
-                                //   timelineDayWidth, timelineGroup, detectDaily, showCompleted,
+                                //   timelineDayWidth, timelineGroup, timelineUpcoming,
+                                //   detectDaily, showCompleted,
                                 //   showIgnored, theme, regionConfirmed, onboarded }
                                 // timelineDayWidth is px per day on the board, stored as the
                                 // measurement rather than a step number and read through
@@ -227,6 +228,10 @@ Namespaced, versioned, and small. Nothing here ever goes to the server.
                                 // timelineGroup is "game" (a lane each) or "ending" (every game
                                 // in one deadline queue). Defaults to "game", so shipping it
                                 // moved nobody's board; see PRD F1.
+                                // timelineUpcoming plots events that have not started yet.
+                                // Defaults to false — the board's window is drawn from what it
+                                // plots, so on by default would push every running bar right to
+                                // make room for things nobody can do yet. See PRD F1.
                                 // knownGames is every lane the reader has been offered. Absent
                                 // means unrecorded, not "offered nothing" — see PRD F8; a lane
                                 // missing from it is new to them and arrives switched off.