feat: PWA push notifications — service worker, VAPID, subscription management

- Add web-push VAPID backend with push_subscriptions table (migration 078)
- Backend push module with sendPushToUser/sendPushToRoom helpers
- Push routes: GET vapid-key, POST subscribe, DELETE unsubscribe
- Trigger push on new chat messages in direct/group rooms
- PWA manifest, service worker, and icons (72–512px)
- Frontend push lib: SW registration, subscribe/unsubscribe helpers
- Push API in api.ts, SW registered in main.tsx
- usePushSubscription hook for auto-subscribe on permission grant
- PushPermissionRow component in ChatWidget settings view

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/chat/ChatWidget.tsx

@@ -7,6 +7,7 @@ import { api, type ChatRoom, type ChatMessage, type ChatSearchResult, type ChatR
 import type { User } from '../../types'
 import { useAuth } from '../../contexts/AuthContext'
 import { cn } from '../../lib/utils'
+import { subscribeToPush, isPushSupported } from '../../lib/push'
 
 // ── Helpers ────────────────────────────────────────────────────────────────
 
@@ -788,6 +789,9 @@ export function ChatWidget() {
                   label="Показывать текст в уведомлении" checked={settings.notifShowText !== false}
                   onChange={v => updateSettings({ notifShowText: v })} />
               </SettingsSection>
+              <SettingsSection title="Push-уведомления">
+                <PushPermissionRow />
+              </SettingsSection>
               <SettingsSection title="Подсказка">
                 <p className="text-xs text-slate-500 leading-relaxed">
                   Правый клик на сообщении — реакции, редактирование, удаление.<br />
@@ -1358,6 +1362,59 @@ function ToggleRow({ icon, label, checked, onChange }: {
   )
 }
 
+// ── PushPermissionRow ─────────────────────────────────────────────────────
+
+function PushPermissionRow() {
+  const [permission, setPermission] = useState<NotificationPermission>(
+    typeof Notification !== 'undefined' ? Notification.permission : 'default'
+  )
+  const [loading, setLoading] = useState(false)
+
+  if (!isPushSupported()) {
+    return (
+      <p className="text-xs text-slate-400 py-2">
+        Ваш браузер не поддерживает push-уведомления.
+        {typeof navigator !== 'undefined' && navigator.userAgent.includes('iPhone') ? ' Добавьте сайт на домашний экран (iOS 16.4+).' : ''}
+      </p>
+    )
+  }
+
+  const enable = async () => {
+    setLoading(true)
+    try {
+      const result = await Notification.requestPermission()
+      setPermission(result)
+      if (result === 'granted') {
+        const { publicKey } = await api.push.getVapidKey()
+        if (!publicKey) return
+        const sub = await subscribeToPush(publicKey)
+        if (!sub) return
+        const json = sub.toJSON()
+        if (json.endpoint && json.keys?.p256dh && json.keys?.auth) {
+          await api.push.subscribe({ endpoint: json.endpoint, p256dh: json.keys.p256dh, auth: json.keys.auth })
+        }
+      }
+    } catch { /**/ }
+    finally { setLoading(false) }
+  }
+
+  return (
+    <div className="flex items-center gap-3 py-2">
+      <span className="text-slate-500 shrink-0"><Bell size={15} /></span>
+      <span className="flex-1 text-sm text-slate-700 dark:text-slate-300 leading-tight">
+        {permission === 'granted' ? 'Push включены' : permission === 'denied' ? 'Заблокированы в браузере' : 'Push-уведомления'}
+      </span>
+      {permission === 'default' && (
+        <button onClick={enable} disabled={loading}
+          className="text-xs px-2.5 py-1 rounded-lg bg-brand-600 text-white hover:bg-brand-700 disabled:opacity-50 transition-colors shrink-0">
+          {loading ? '...' : 'Включить'}
+        </button>
+      )}
+      {permission === 'granted' && <span className="text-xs text-green-500 shrink-0">✓</span>}
+    </div>
+  )
+}
+
 // ── GroupInfoView ──────────────────────────────────────────────────────────
 
 function GroupInfoView({ room, allMembers, currentUserId, saving, editName, onEditName, onAvatarClick, onSave }: {