feat(permission): redesign first-run grant-access screen (M3 Expressive)

The onboarding screen is the first thing a new user sees; it was a bare
centred title + body + button. Rebuild it as a proper Material 3 Expressive
welcome:

- Branded hero reconstructing the launcher mark (slate squircle + foreground
  vector); the denied state adds a lock badge over the corner
- App-name eyebrow, a benefit-led headline, and three trust rows (stays on
  device / every calendar together / no tracking) with tonal icon chips
- Full-width filled CTA with a trailing arrow, pinned in a Scaffold bottom bar
  clear of the navigation bar; scrollable body for short screens
- "Read-only · no internet permission" footnote — accurate: the app declares
  only READ_CALENDAR
- Denied/recovery state reuses the same shell with Open-settings (primary) and
  Try-again (text) actions
- 8dp spacing scale, edge-to-edge insets handled via Scaffold

Built with the newly installed material-3 skill's token/component guidance.
Resolves the pre-1.0 polish backlog item.

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

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

@@ -12,13 +12,20 @@
     <string name="state_failure_provider">Kalender konnte nicht gelesen werden.</string>
 
     <!-- Permission-Flow (F1) -->
-    <string name="permission_rationale_title">Kalender-Zugriff</string>
-    <string name="permission_rationale_body">Calendula liest nur deinen Gerätekalender — keine Daten verlassen das Gerät.</string>
-    <string name="permission_request_button">Weiter</string>
+    <string name="permission_rationale_title">Alle Termine, schön im Blick</string>
+    <string name="permission_rationale_body">Calendula braucht Lesezugriff auf deinen Kalender, um deine Termine zu zeigen. Mehr verlangt die App nie.</string>
+    <string name="permission_request_button">Kalender-Zugriff erlauben</string>
     <string name="permission_denied_title">Kalender-Zugriff abgelehnt</string>
     <string name="permission_denied_body">Ohne Kalender-Zugriff kann Calendula keine Termine anzeigen. Du kannst den Zugriff in den System-Einstellungen wieder erlauben.</string>
     <string name="permission_open_settings_button">System-Einstellungen öffnen</string>
     <string name="permission_retry_button">Erneut versuchen</string>
+    <string name="permission_benefit_private_title">Bleibt auf deinem Gerät</string>
+    <string name="permission_benefit_private_body">Deine Kalender werden lokal gelesen und verlassen das Telefon nie.</string>
+    <string name="permission_benefit_sync_title">Alle Kalender vereint</string>
+    <string name="permission_benefit_sync_body">Google, CalDAV, lokal — alles, was synchronisiert ist, erscheint automatisch.</string>
+    <string name="permission_benefit_privacy_title">Kein Tracking, niemals</string>
+    <string name="permission_benefit_privacy_body">Keine Telemetrie, keine Analyse, keine Werbung.</string>
+    <string name="permission_privacy_footnote">Nur Lesezugriff · keine Internet-Berechtigung</string>
 
     <!-- Monatsansicht (S1) -->
     <string name="month_prev">Vorheriger Monat</string>