feat: realtime sync, settings UX and chat list improvements

- add chat_updated realtime event and dynamic chat subscriptions

- auto-join invite links in web app

- implement Telegram-like settings panel (general/notifications/privacy)

- add browser notification preferences and keyboard send mode

- improve chat list with last message preview/time and online badge

- rework chat members UI with context actions and role crowns

web/src/utils/preferences.ts

@@ -0,0 +1,87 @@
+export type ThemeMode = "light" | "dark" | "system";
+export type SendMode = "enter" | "ctrl_enter";
+
+export interface AppPreferences {
+  theme: ThemeMode;
+  messageFontSize: number;
+  sendMode: SendMode;
+  webNotifications: boolean;
+  privateNotifications: boolean;
+  groupNotifications: boolean;
+  channelNotifications: boolean;
+  messagePreview: boolean;
+}
+
+const STORAGE_KEY = "bm_preferences_v1";
+
+const DEFAULTS: AppPreferences = {
+  theme: "system",
+  messageFontSize: 16,
+  sendMode: "enter",
+  webNotifications: true,
+  privateNotifications: true,
+  groupNotifications: true,
+  channelNotifications: true,
+  messagePreview: true,
+};
+
+export function getAppPreferences(): AppPreferences {
+  if (typeof window === "undefined") {
+    return DEFAULTS;
+  }
+  try {
+    const raw = window.localStorage.getItem(STORAGE_KEY);
+    if (!raw) {
+      return DEFAULTS;
+    }
+    const parsed = JSON.parse(raw) as Partial<AppPreferences>;
+    return {
+      theme: parsed.theme === "light" || parsed.theme === "dark" || parsed.theme === "system" ? parsed.theme : DEFAULTS.theme,
+      messageFontSize: normalizeFontSize(parsed.messageFontSize),
+      sendMode: parsed.sendMode === "ctrl_enter" ? "ctrl_enter" : "enter",
+      webNotifications: typeof parsed.webNotifications === "boolean" ? parsed.webNotifications : DEFAULTS.webNotifications,
+      privateNotifications: typeof parsed.privateNotifications === "boolean" ? parsed.privateNotifications : DEFAULTS.privateNotifications,
+      groupNotifications: typeof parsed.groupNotifications === "boolean" ? parsed.groupNotifications : DEFAULTS.groupNotifications,
+      channelNotifications: typeof parsed.channelNotifications === "boolean" ? parsed.channelNotifications : DEFAULTS.channelNotifications,
+      messagePreview: typeof parsed.messagePreview === "boolean" ? parsed.messagePreview : DEFAULTS.messagePreview,
+    };
+  } catch {
+    return DEFAULTS;
+  }
+}
+
+export function saveAppPreferences(next: AppPreferences): void {
+  if (typeof window === "undefined") {
+    return;
+  }
+  window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
+}
+
+export function updateAppPreferences(patch: Partial<AppPreferences>): AppPreferences {
+  const current = getAppPreferences();
+  const next: AppPreferences = {
+    ...current,
+    ...patch,
+    messageFontSize: normalizeFontSize((patch.messageFontSize ?? current.messageFontSize)),
+  };
+  saveAppPreferences(next);
+  applyAppearancePreferences(next);
+  return next;
+}
+
+export function applyAppearancePreferences(prefs: AppPreferences): void {
+  if (typeof document === "undefined") {
+    return;
+  }
+  document.documentElement.style.setProperty("--bm-font-size", `${prefs.messageFontSize}px`);
+  document.documentElement.setAttribute("data-theme", prefs.theme);
+}
+
+function normalizeFontSize(value: number | undefined): number {
+  const input = Number(value);
+  if (!Number.isFinite(input)) {
+    return DEFAULTS.messageFontSize;
+  }
+  return Math.max(12, Math.min(24, Math.round(input)));
+}
+