feat(settings): Preferences notification-badge picker

Closes out the Behavior subsection. Uses NotificationBadgeStyle
(None/Unread Indicator/Unread Count) — wire values are a guess same as
the other preference keys, flagged in OutlineUserPreferences.

Outpost/Features/Account/SettingsView.swift

@@ -293,6 +293,8 @@ struct SettingsView: View {
                     isOn: session.userPreferences?.smartText ?? false,
                     onChange: { newValue in Task { await savePreference { $0.smartText = newValue } } }
                 )
+                Divider()
+                notificationBadgeRow
             }
 
             if let preferencesErrorMessage {
@@ -370,6 +372,34 @@ struct SettingsView: View {
         }
     }
 
+    private var notificationBadgeRow: some View {
+        HStack {
+            VStack(alignment: .leading, spacing: 2) {
+                Text("Notification badge")
+                Text("Choose how unread notifications are indicated on the app icon.")
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+            }
+            Spacer()
+            Picker("Notification badge", selection: notificationBadgeBinding) {
+                ForEach(NotificationBadgeStyle.allCases) { style in
+                    Text(style.label).tag(style)
+                }
+            }
+            .labelsHidden()
+            .frame(width: 160)
+        }
+    }
+
+    private var notificationBadgeBinding: Binding<NotificationBadgeStyle> {
+        Binding(
+            get: {
+                session.userPreferences?.notificationBadge.flatMap(NotificationBadgeStyle.init(rawValue:)) ?? .all
+            },
+            set: { newValue in Task { await savePreference { $0.notificationBadge = newValue.rawValue } } }
+        )
+    }
+
     private var languageBinding: Binding<String> {
         Binding(
             get: { session.userLanguage ?? "en_US" },