docs: where the unstarted-events switch lives, and why there

F1 described a control in the board's header that is now a row in
settings, and the reasoning is worth keeping rather than the location
alone: the header holds the controls that reshape what is on the board,
settings holds the ones that decide what is on it. That is the line, and
it is what would otherwise be re-argued the next time a filter needs a
home.

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

docs/DATA-MODEL.md

@@ -231,7 +231,9 @@ Namespaced, versioned, and small. Nothing here ever goes to the server.
                                 // 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.
+                                // make room for things nobody can do yet. Set from settings
+                                // alongside showCompleted / showIgnored, and the only one of
+                                // the three scoped to one view. 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.

docs/PRD.md

@@ -117,10 +117,16 @@ all of it unasked stretched the window weeks past today and squeezed the running
 came for down to nothing. `prefs.timelineUpcoming` defaults to `false`, which is what every existing
 board already looked like on the day it shipped, since the window is drawn from what is plotted.
 Nothing is hidden by that: the checklist's own "Not started yet" section (F2) has listed them all
-along, and the control on the board says **how many** are being held back rather than leaving them
-as an absence. A board with nothing running says exactly that, and points at the control, instead of
+along, and a board with nothing left running says exactly that and names the setting, instead of
 reading as an empty calendar.
 
+The switch is in settings (F4), with the two other answers to *what am I allowed to look at* —
+`showCompleted` and `showIgnored` — and **not** in the board's own header beside the stacking and
+scale controls. That is the line those two draw: they reshape what is already on the board, which is
+why they are reached for while reading it, and this one decides what is on it at all. It is the only
+one of the three scoped to a single view, so its row says so rather than reading as a promise about
+the whole app.
+
 **Switched on, the board says in words where they begin.** A bar drawn to the right of the "now"
 rule is only *implicitly* in the future, and implicitly is not a standard this product holds itself
 to anywhere else a date is involved. Gacha schedules are not a smooth stream of start dates either —