refactor(timeline): move the unstarted-events switch into settings

It shipped as a pill in the board's own header, beside the stacking and
scale controls. That is the wrong company: those two 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 — the same question
"Show events I've finished" and "Show events I'm ignoring" answer, from
the panel where both of those live.

It is the only one of the three scoped to a single view, so the row says
so instead of reading as a promise about the whole app. The board loses
the count the pill carried; with nothing left running it still says how
many are waiting and names the setting, and the page header has said
"N live · N upcoming" all along.

Controls had no tests at all, so the three view filters get some: what
each checkbox is bound to is invisible in a diff and obvious only to the
reader it happens to.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/client/components/Timeline.tsx

@@ -98,7 +98,6 @@ export function Timeline({
   group,
   onGroup,
   showUpcoming,
-  onShowUpcoming,
   onOpen,
   isDone,
 }: {
@@ -116,11 +115,15 @@ export function Timeline({
    * Off by default (`prefs.timelineUpcoming`). The board is asked "how does the
    * time I am in lay out?", and every lane has a next patch queued behind it —
    * plotting those unasked stretches the window weeks past today and squeezes
-   * the running bars the reader came for. The count is on the control, so what
-   * is held back is stated rather than merely absent.
+   * the running bars the reader came for.
+   *
+   * Read-only here: the switch lives in settings with the other two answers to
+   * "what am I allowed to look at" (`Controls`), not in the board's own header
+   * beside the stacking and scale controls. Those two reshape what is already
+   * on the board, which is why they are reached for while reading it; this one
+   * decides what is on it at all.
    */
   showUpcoming: boolean;
-  onShowUpcoming: (showUpcoming: boolean) => void;
   onOpen: (id: string) => void;
   /**
    * Asked rather than derived from the progress store: an entry exists there
@@ -213,14 +216,7 @@ export function Timeline({
           floating over the chart: pinned inside, it would sit on top of the
           calendar and cover the very dates it sends you back to. */}
       <div className="flex flex-wrap items-center justify-between gap-x-3 gap-y-2 border-b border-hairline px-4 py-2.5">
-        <div className="flex items-center gap-2">
-          <StackControl value={group} onChange={onGroup} />
-          <UpcomingControl
-            on={showUpcoming}
-            waiting={waiting.length}
-            onChange={onShowUpcoming}
-          />
-        </div>
+        <StackControl value={group} onChange={onGroup} />
 
         <div className="flex items-center gap-3">
           <div role="group" aria-label="Scale" className="flex items-center gap-1">
@@ -259,7 +255,8 @@ export function Timeline({
           {waiting.length === 1
             ? "One event has not started yet"
             : `${waiting.length} events have not started yet`}{" "}
-          — switch “Not started” on to see when they begin.
+          — switch on “Show events that haven't started” below to see when they
+          begin.
         </p>
       ) : (
       <div
@@ -541,50 +538,6 @@ function StackControl({
   );
 }
 
-/**
- * Whether the board also plots what has not started yet.
- *
- * A switch rather than a third stacking pill, and drawn as one — it does not
- * reshape the board, it changes what is on it. The count is the point: a board
- * that quietly withheld nine events would be indistinguishable from a quiet
- * fortnight, and "nothing scheduled" is exactly the wrong thing for this app to
- * imply by accident.
- *
- * Absent when there is nothing waiting and it is switched off: a toggle that
- * cannot change anything invites a tap that does nothing.
- */
-function UpcomingControl({
-  on,
-  waiting,
-  onChange,
-}: {
-  on: boolean;
-  waiting: number;
-  onChange: (on: boolean) => void;
-}) {
-  if (waiting === 0 && !on) return null;
-  return (
-    <button
-      type="button"
-      onClick={() => onChange(!on)}
-      aria-pressed={on}
-      title={
-        on
-          ? "Stop plotting events that have not started yet"
-          : "Also plot events that have not started yet"
-      }
-      className={`flex items-center gap-1.5 rounded-full border px-2.5 py-1 text-[0.6875rem] font-medium transition-colors ${
-        on
-          ? "border-ink/60 text-ink"
-          : "border-hairline text-faint hover:text-muted"
-      }`}
-    >
-      Not started
-      <span className="tnum text-[0.625rem] text-faint">{waiting}</span>
-    </button>
-  );
-}
-
 /**
  * One step of the scale control.
  *