feat(web): service-worker notifications and composer/scroll UX fixes

- register notifications service worker and handle click-to-open chat/message

- route realtime notifications through service worker with fallback

- support ?chat=&message= deep-link navigation in chats page

- enforce 1s minimum voice message length

- lift scroll-to-bottom button to avoid overlap with composer action

web/src/utils/webNotifications.ts

@@ -0,0 +1,84 @@
+import type { Message } from "../chat/types";
+
+export async function registerNotificationServiceWorker(): Promise<void> {
+  if (typeof window === "undefined" || !("serviceWorker" in navigator)) {
+    return;
+  }
+  try {
+    await navigator.serviceWorker.register("/notifications-sw.js");
+  } catch {
+    return;
+  }
+}
+
+export async function showNotificationViaServiceWorker(params: {
+  chatId: number;
+  messageId: number;
+  title: string;
+  body: string;
+  image?: string;
+}): Promise<boolean> {
+  if (typeof window === "undefined" || !("serviceWorker" in navigator)) {
+    return false;
+  }
+  try {
+    const registration = await navigator.serviceWorker.getRegistration();
+    if (!registration) {
+      return false;
+    }
+    const url = `/?chat=${params.chatId}&message=${params.messageId}`;
+    await registration.showNotification(params.title, {
+      body: params.body,
+      icon: params.image,
+      tag: `chat-${params.chatId}`,
+      data: {
+        chatId: params.chatId,
+        messageId: params.messageId,
+        url,
+      },
+    });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export function messagePreviewByType(type: Message["type"]): string {
+  if (type === "image") return "Photo";
+  if (type === "video") return "Video";
+  if (type === "audio") return "Audio";
+  if (type === "voice") return "Voice message";
+  if (type === "file") return "File";
+  if (type === "circle_video") return "Video message";
+  return "New message";
+}
+
+export function buildNotificationPreview(
+  message: Message,
+  withPreview: boolean
+): { body: string; image?: string } {
+  if (!withPreview) {
+    return { body: "New message" };
+  }
+  if (message.type !== "text") {
+    if (message.type === "image") {
+      const imageUrl = typeof message.text === "string" && isLikelyUrl(message.text) ? message.text : undefined;
+      return { body: "🖼 Photo", image: imageUrl };
+    }
+    return { body: messagePreviewByType(message.type) };
+  }
+  const text = message.text?.trim();
+  if (!text) {
+    return { body: "New message" };
+  }
+  return { body: text };
+}
+
+function isLikelyUrl(value: string): boolean {
+  try {
+    const parsed = new URL(value);
+    return parsed.protocol === "http:" || parsed.protocol === "https:";
+  } catch {
+    return false;
+  }
+}