#10 add group chat delete alongside leave

- Delete a group chat from GroupInfoView or via a swipe in the chat
  list: remove the conversation and its messages from SwiftData,
  clean per-chat state, and leave the room on the server first when
  joined.
- Keep "Покинуть комнату" as leave-without-deleting and suppress
  deleted rooms for the session so roomState events cannot recreate
  them; an explicit rejoin or a fresh invitation clears the
  suppression.
- Add verify.sh invariants and document the behaviour in
  ARCHITECTURE.md.

Sources/Shared/UI/GroupInfoView.swift

@@ -11,6 +11,7 @@ struct GroupInfoView: View {
     @State private var invitees = ""
     @State private var isJoining = false
     @State private var isInviting = false
+    @State private var confirmingDeletion = false
 
     init(model: AppModel, conversation: Conversation) {
         self.model = model
@@ -68,6 +69,16 @@ struct GroupInfoView: View {
                     }
                 }
 
+                Section {
+                    Button(role: .destructive) {
+                        confirmingDeletion = true
+                    } label: {
+                        Label("Удалить чат", systemImage: "trash")
+                    }
+                } footer: {
+                    Text("Чат и его история будут удалены с этого устройства.")
+                }
+
                 Section {
                     Label(
                         model.encryptionEnabled(for: conversation.jid)
@@ -85,6 +96,15 @@ struct GroupInfoView: View {
                     Button("Готово") { dismiss() }
                 }
             }
+            .alert("Удалить групповой чат?", isPresented: $confirmingDeletion) {
+                Button("Удалить", role: .destructive) {
+                    model.deleteGroupChat(jid: conversation.jid)
+                    dismiss()
+                }
+                Button("Отмена", role: .cancel) {}
+            } message: {
+                Text("Чат и его история будут удалены с этого устройства. Luma выйдет из комнаты, если вы в ней.")
+            }
         }
 #if os(macOS)
         .frame(minWidth: 480, minHeight: 500)