feat: per-user notification preference toggles

Add per-namespace notification preferences so users can choose which
event types trigger push notifications (permission requests, session
ready, task notifications, session completion). Adds the
notification_preferences table (schema v20), GET/PUT
/api/notification-preferences, POST /api/push/test for test pushes, and
a Notifications settings page in the web app with a confirm dialog for
disabling permission requests. Defaults keep all event types enabled.

via [HAPI](https://hapi.run)

Co-Authored-By: HAPI <noreply@hapi.run>
Co-Authored-By: Claude <noreply@anthropic.com>

web/src/types/api.ts

@@ -176,6 +176,23 @@ export type PushVapidPublicKeyResponse = {
     publicKey: string
 }
 
+export type NotificationPreferences = {
+    namespace: string
+    permissionRequests: number
+    sessionReady: number
+    taskNotifications: number
+    sessionCompletion: number
+    updatedAt: number
+}
+
+export type NotificationPreferencesUpdate = Partial<
+    Pick<NotificationPreferences, 'permissionRequests' | 'sessionReady' | 'taskNotifications' | 'sessionCompletion'>
+>
+
+export type TestPushResponse =
+    | { ok: true }
+    | { error: string }
+
 export type CodexDesktopScriptResponse = {
     success: boolean
     message?: string