feat(widget): apply the past-event display setting to the agenda widget

Issue #12 asks for hiding finished events in the agenda view *and* its
home-screen widget. The in-app screen already honours the Past events
setting (Show / Dim / Hide); extend the same setting to the "Upcoming"
agenda widget.

The widget loads its events unfiltered and applies the mode reactively in
the composition against a captured "now" — mirroring how the range is read
from per-instance Glance state — so toggling the setting reflects on a live
widget without relying on provideGlance's data preamble re-running. Hiding
drops finished events and any day they empty; dimming fades the colour
stripe and lowers the title's emphasis (Glance has no generic alpha
modifier). setPastEventDisplay now pushes the mode into each widget's Glance
state and recomposes, like setAgendaWidgetRange.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -10,12 +10,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - See past events your way. Two new settings change how events that have already
   ended are shown. **Past events** (Settings → Appearance → Agenda) lets the
-  agenda keep them as usual, dim them, or hide them from the list entirely.
-  **Dim completed events** (Settings → Appearance) separately fades finished
-  events in the month and week views. Both are off by default, an event only
-  counts as finished once it has actually ended (events still in progress are
-  never dimmed), and the list updates on its own as the day goes on. Thanks to
-  @ptab for the suggestion ([#12]).
+  agenda — both in the app and the home-screen "Upcoming" widget — keep them as
+  usual, dim them, or hide them from the list entirely. **Dim completed events**
+  (Settings → Appearance) separately fades finished events in the month and week
+  views. Both are off by default, an event only counts as finished once it has
+  actually ended (events still in progress are never dimmed), and the lists
+  update on their own as the day goes on. Thanks to @ptab for the suggestion
+  ([#12]).
 
 ### Changed
 - Readable titles on overlapping events. In the week and day views, events that