Merge tag '2025.4.0' into merge/2025-03-24

# Conflicts:
#	.github/workflows/storybook.yml
#	locales/index.d.ts
#	package.json
#	packages/backend/src/models/json-schema/role.ts
#	packages/frontend/src/components/MkPageWindow.vue
#	packages/frontend/src/pages/admin/roles.editor.vue
#	packages/frontend/src/pages/admin/roles.vue
#	packages/frontend/src/pages/settings/preferences.vue
#	packages/frontend/src/pages/settings/privacy.vue
#	packages/frontend/src/pages/timeline.vue
#	packages/frontend/src/pref-migrate.ts
#	packages/frontend/src/ui/_common_/common.vue
#	packages/frontend/src/ui/deck.vue
#	packages/frontend/src/ui/universal.vue
#	packages/misskey-js/src/autogen/types.ts

packages/frontend/src/navbar.ts

@@ -134,6 +134,7 @@ export const navbarItemDef = reactive({
 		title: i18n.ts.chat,
 		icon: 'ti ti-messages',
 		to: '/chat',
+		show: computed(() => $i != null && $i.policies.chatAvailability !== 'unavailable'),
 		indicated: computed(() => $i != null && $i.hasUnreadChatMessages),
 	},
 	achievements: {