feat(detail): full-screen event detail (S4) with humanized recurrence

Tapping an event in the week/day timeline opens a full-screen detail
destination (MD3 list→detail, not a bottom sheet) overlaying the calendar
with a slide transition. One card per field (when, calendar, location,
description, attendees, recurrence) with leading icons; location taps open
a maps intent. Loading/Failure/Success throughout.

Recurrence is humanized from the RRULE — e.g. "Every week on Tue and Thu
until 31 Dec 2026" — covering FREQ/INTERVAL/BYDAY/UNTIL/COUNT with
abbreviated, italicised day names and localized list formatting, falling
back to a generic label for rules it can't render.

Also:
- fix: recurring events failed to open (series row stores DURATION, not
  DTEND, so the mapper dropped them as EventNotFound). The detail keeps
  them and shows the tapped occurrence's own times from Instances.
- feat: month day cell → opens the day view anchored to that date.
- build: add material-icons-extended (R8 strips unused icons in release).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -38,6 +38,36 @@
     <!-- Tagesansicht (S3) -->
     <string name="day_today_action">Heute</string>
 
+    <!-- Event-Detail-Screen (S4) -->
+    <string name="event_detail_back">Zurück</string>
+    <string name="event_detail_edit">Bearbeiten</string>
+    <string name="event_detail_delete">Löschen</string>
+    <string name="event_detail_all_day">Ganztägig</string>
+    <string name="event_detail_calendar">Kalender</string>
+    <string name="event_detail_calendar_unknown">Unbekannter Kalender</string>
+    <string name="event_detail_location">Ort</string>
+    <string name="event_detail_description">Beschreibung</string>
+    <string name="event_detail_attendees">Teilnehmer</string>
+    <string name="event_detail_recurrence">Wiederholung</string>
+    <string name="event_detail_recurring">Wiederkehrender Termin</string>
+    <string name="recurrence_daily">Jeden Tag</string>
+    <string name="recurrence_weekly">Jede Woche</string>
+    <string name="recurrence_monthly">Jeden Monat</string>
+    <string name="recurrence_yearly">Jedes Jahr</string>
+    <string name="recurrence_every_n_days">Alle %1$d Tage</string>
+    <string name="recurrence_every_n_weeks">Alle %1$d Wochen</string>
+    <string name="recurrence_every_n_months">Alle %1$d Monate</string>
+    <string name="recurrence_every_n_years">Alle %1$d Jahre</string>
+    <string name="recurrence_on_days">%1$s am %2$s</string>
+    <string name="recurrence_with_until">%1$s bis %2$s</string>
+    <string name="recurrence_with_count">%1$s, %2$d Mal</string>
+    <string name="event_detail_not_found">Dieser Termin existiert nicht mehr.</string>
+    <string name="event_attendee_accepted">Zugesagt</string>
+    <string name="event_attendee_declined">Abgesagt</string>
+    <string name="event_attendee_tentative">Vorläufig</string>
+    <string name="event_attendee_needs_action">Keine Antwort</string>
+    <string name="event_attendee_unknown">—</string>
+
     <!-- Geteilte Event-Strings -->
     <string name="event_untitled">(Ohne Titel)</string>