fix(screensaver): keep both screen saver activities out of the app's task

The settings screen Android's screen saver list opens gets a task of its
own and stays out of recents, so it never lands in or clears the app's
task, and its bars follow the app's theme. The on-demand screen saver is
noHistory, so leaving it by Home does not bring the app back to it later,
and it only touches the keep-screen-on flag when charging starts or stops.

The next-alarm line uses the same 12/24-hour rule as the big readout,
joined to the day by a translatable string; the minute's crossfade shows
the old minute fading out rather than two copies of the new one.

app/src/main/res/values/strings.xml

@@ -315,6 +315,8 @@
     <string name="screen_saver_system_settings_hint">Pick Clockula as the screen saver in Android\'s settings</string>
     <!-- Read by a screen reader for the alarm line on the screen saver; %1$s is the day and time, "Tue 7:00 AM". -->
     <string name="screen_saver_next_alarm">Next alarm: %1$s</string>
+    <!-- The screen saver's next-alarm line: %1$s is the day ("Tue", or "Thu, Oct 29" a week or more away), %2$s the time ("7:00 AM"). -->
+    <string name="screen_saver_next_alarm_when">%1$s %2$s</string>
     <string name="menu_more_options">More options</string>
     <string name="settings_self_check">Why might my alarm not ring?</string>
     <string name="settings_self_check_title">Why might my alarm not ring?</string>