feat(settings): Preferences separate-editing toggle

Starts the Behavior subsection.

Outpost/Features/Account/SettingsView.swift

@@ -272,6 +272,15 @@ struct SettingsView: View {
                 )
             }
 
+            preferencesSubsection("Behavior") {
+                preferenceToggleRow(
+                    "Separate editing",
+                    description: "When enabled, documents have a separate editing mode. When disabled, documents are always editable when you have permission.",
+                    isOn: session.userPreferences?.separateEditing ?? false,
+                    onChange: { newValue in Task { await savePreference { $0.separateEditing = newValue } } }
+                )
+            }
+
             if let preferencesErrorMessage {
                 Text(preferencesErrorMessage)
                     .font(.caption)