feat: iOS Sharing + iCal Import/Export für lokale Kalender

Kalenderverwaltung: pro lokalem Kalender ein Menü mit Teilen (SharingView:
Benutzer aus Verzeichnis, read/read_write, entfernbar), Importieren
(.ics File Picker) und Exportieren (Share Sheet). Geteilte Kalender mit
"geteilt von"-Badge; Gruppenkalender markiert.

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

Calendarr iOS/Models/Localization.swift

@@ -140,6 +140,20 @@ private let strings: [String: [String: String]] = [
         "group.visible.none": "Keiner",
         "profile.display_name": "Anzeigename",
         "profile.login_name": "Login-Name",
+        "accounts.shared_by": "geteilt von %@",
+        "share.title": "Teilen",
+        "share.current": "Aktuelle Freigaben",
+        "share.none": "Noch nicht geteilt",
+        "share.add": "Benutzer hinzufügen",
+        "share.search": "Benutzer suchen…",
+        "share.permission": "Berechtigung",
+        "perm.read": "Nur lesen",
+        "perm.read_write": "Lesen & schreiben",
+        "ics.import": "Importieren",
+        "ics.export": "Exportieren",
+        "ics.import_result": "%d importiert, %d übersprungen",
+        "common.info": "Info",
+        "common.done": "Fertig",
 
         "settings.hourheight": "Stundenhöhe",
         "settings.hourheight.desc": "Platz pro Stunde in der Wochen- & Tagesansicht",
@@ -415,6 +429,20 @@ private let strings: [String: [String: String]] = [
         "group.visible.none": "None",
         "profile.display_name": "Display name",
         "profile.login_name": "Login name",
+        "accounts.shared_by": "shared by %@",
+        "share.title": "Share",
+        "share.current": "Current shares",
+        "share.none": "Not shared yet",
+        "share.add": "Add user",
+        "share.search": "Search users…",
+        "share.permission": "Permission",
+        "perm.read": "Read only",
+        "perm.read_write": "Read & write",
+        "ics.import": "Import",
+        "ics.export": "Export",
+        "ics.import_result": "%d imported, %d skipped",
+        "common.info": "Info",
+        "common.done": "Done",
 
         "settings.hourheight": "Hour height",
         "settings.hourheight.desc": "Space per hour in week & day view",