feat(agenda): warmer empty state + "upcoming" wording

Reword the range header to "Showing all upcoming events for". Replace the
dry empty state ("Nothing scheduled" + subtitle) with a single warmer line
("You're all caught up"), drop the subtitle, and switch the icon to a
coffee cup. The empty title is shared with the agenda widget.

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

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

@@ -230,8 +230,7 @@
     <string name="agenda_today_action">Heute</string>
     <string name="agenda_header_today">Heute</string>
     <string name="agenda_header_tomorrow">Morgen</string>
-    <string name="agenda_empty_title">Nichts geplant</string>
-    <string name="agenda_empty_subtitle">Anstehende Termine erscheinen hier.</string>
+    <string name="agenda_empty_title">Alles erledigt</string>
 
     <!-- Terminsuche -->
     <string name="search_action">Suchen</string>
@@ -298,7 +297,7 @@
     <string name="agenda_range_custom">Benutzerdefiniert…</string>
     <string name="agenda_range_custom_hint">Tage</string>
     <string name="agenda_range_override_hint">Nur vorübergehend — wird beim erneuten Öffnen von Calendula auf deinen gespeicherten Zeitraum zurückgesetzt.</string>
-    <string name="agenda_range_showing_label">Alle Termine für</string>
+    <string name="agenda_range_showing_label">Alle anstehenden Termine für</string>
     <plurals name="agenda_range_days">
         <item quantity="one">%d Tag</item>
         <item quantity="other">%d Tage</item>

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

@@ -231,8 +231,7 @@
     <string name="agenda_today_action">Today</string>
     <string name="agenda_header_today">Today</string>
     <string name="agenda_header_tomorrow">Tomorrow</string>
-    <string name="agenda_empty_title">Nothing scheduled</string>
-    <string name="agenda_empty_subtitle">Upcoming events will show up here.</string>
+    <string name="agenda_empty_title">You\'re all caught up</string>
 
     <!-- Event search -->
     <string name="search_action">Search</string>
@@ -291,7 +290,7 @@
     <string name="agenda_range_custom">Custom…</string>
     <string name="agenda_range_custom_hint">Days</string>
     <string name="agenda_range_override_hint">Just for now — resets to your saved range when you reopen Calendula.</string>
-    <string name="agenda_range_showing_label">Showing all events for</string>
+    <string name="agenda_range_showing_label">Showing all upcoming events for</string>
     <plurals name="agenda_range_days">
         <item quantity="one">%d day</item>
         <item quantity="other">%d days</item>