feat(widgets): let each widget pick its theme and wallpaper colours

Every widget instance can now follow the system or be pinned to Light or
Dark, and on Android 12+ turn the wallpaper's colours off in favour of
the app's own palette. Both are set in the widget's config screen and
stored in its own Glance state; an instance without them keeps today's
look.

Glance content takes them through WidgetTheme. The plain-RemoteViews
parts (the analog and digital faces, readouts and chronometers) go
through a new WidgetPalette, which resolves the widget_* palette under a
forced day/night and sets concrete colours, or day/night pairs, on the
views. The app's own tones are now widget_app_*, so they stay reachable
on API 31+. The analog and digital clocks are re-coloured on API 31+
only: below that AnalogClock's hands and a shape's background tint can't
be set through RemoteViews, so their config screens don't offer it.

The next-alarm and timer widgets gain a config screen for this
(configuration_optional, so placing one doesn't stop there). The analog,
stopwatch and quick-timer config screens become settings screens with an
OK, like the digital clock's, since they now hold more than one choice.

Background opacity is left out: most faces are a shape with text in its
container colour rather than a card, so there is no background to fade
without losing contrast against the wallpaper.

Closes #6

app/src/main/AndroidManifest.xml

@@ -318,6 +318,25 @@
             </intent-filter>
         </activity>
 
+        <!-- The next-alarm and timer widgets' per-instance colours: the same
+             APPWIDGET_CONFIGURE contract as the four above. -->
+        <activity
+            android:name=".ui.widget.config.NextAlarmConfigActivity"
+            android:exported="true"
+            android:theme="@style/Theme.Clockula">
+            <intent-filter>
+                <action android:name="android.appwidget.action.APPWIDGET_CONFIGURE" />
+            </intent-filter>
+        </activity>
+        <activity
+            android:name=".ui.widget.config.TimerConfigActivity"
+            android:exported="true"
+            android:theme="@style/Theme.Clockula">
+            <intent-filter>
+                <action android:name="android.appwidget.action.APPWIDGET_CONFIGURE" />
+            </intent-filter>
+        </activity>
+
         <!-- The quick-timer widget's one tap: creates and starts a timer at
              its configured duration. A broadcast, not a service start or an
              activity, for the same reason as `TimerActionReceiver` (M11 D16). -->