fix(webui): sync file edit display preference

webui/src/lib/local-preferences.ts

@@ -11,6 +11,7 @@ export interface LocalPreferences {
 }
 
 export const LOCAL_PREFS_STORAGE_KEY = "nanobot-webui.settings-preferences";
+export const LOCAL_PREFS_CHANGED_EVENT = "nanobot-webui.local-preferences-changed";
 
 export const DEFAULT_LOCAL_PREFS: LocalPreferences = {
   density: "comfortable",
@@ -40,3 +41,15 @@ export function readLocalPreferences(): LocalPreferences {
     return DEFAULT_LOCAL_PREFS;
   }
 }
+
+export function writeLocalPreferences(preferences: LocalPreferences): void {
+  try {
+    window.localStorage.setItem(LOCAL_PREFS_STORAGE_KEY, JSON.stringify(preferences));
+  } catch {
+    // Browser-only preferences should never block settings.
+  }
+  window.dispatchEvent(new CustomEvent<LocalPreferences>(
+    LOCAL_PREFS_CHANGED_EVENT,
+    { detail: preferences },
+  ));
+}