feat(sharing): hidden-profile toggle + hide non-sharing group members

- UserProfile decodes directory_hidden; updateProfile() sends it; Settings has
  a "hide my profile" toggle (excludes you from share/group pickers).
- GroupMember decodes shares_calendar; the group filter list now only shows
  members who actually share a calendar (no phantom empty rows).
- Robust custom decoders (decodeIfPresent) for the new fields.

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

Calendarr iOS/Models/Localization.swift

@@ -132,6 +132,8 @@ private let strings: [String: [String: String]] = [
         "settings.privacy": "Privatsphäre",
         "settings.private_visibility": "Private Termine für Gruppen",
         "settings.private_visibility.desc": "Wie private Termine für andere Gruppenmitglieder erscheinen",
+        "settings.directory_hidden": "Profil verbergen",
+        "settings.directory_hidden.desc": "Nicht in Teilen-/Gruppen-Auswahl anzeigen. In der Admin-Benutzerverwaltung bleibst du sichtbar.",
         "settings.private.busy": "Als „Beschäftigt“",
         "settings.private.hidden": "Ausblenden",
         "settings.calendars": "Geteilter Kalender",
@@ -461,6 +463,8 @@ private let strings: [String: [String: String]] = [
         "settings.privacy": "Privacy",
         "settings.private_visibility": "Private events for groups",
         "settings.private_visibility.desc": "How your private events appear to other group members",
+        "settings.directory_hidden": "Hide my profile",
+        "settings.directory_hidden.desc": "Don't show me in share/group pickers. You stay visible in the admin user management.",
         "settings.private.busy": "Show as \"Busy\"",
         "settings.private.hidden": "Hide",
         "settings.calendars": "Shared calendar",