feat: add notification suppression rules (#1525)

* feat: add notification suppression rules

* fix: restore label routing and routing test mocks for suppression

* fix: allow bell mute shortcuts for history-only notification categories

Suppression rule validation used the routable category whitelist, which rejected history-only categories such as update_started that appear in the bell during stack updates.

* feat: expand Mute Rules UX with compose-first entry points and activity badges

* fix: add missing NodeContext mocks for notification suppression tests

frontend/src/components/settings/registry.ts

@@ -220,6 +220,17 @@ export const SETTINGS_ITEMS: readonly SettingsItemMeta[] = [
         adminOnly: true,
         hiddenOnRemote: true,
     },
+    {
+        id: 'notification-suppression',
+        group: 'notifications',
+        label: 'Mute Rules',
+        description: 'Mute or drop matching alerts from the bell, external channels, or both.',
+        keywords: ['mute', 'suppress', 'silence', 'hide', 'bell', 'rules'],
+        tier: null,
+        scope: 'global',
+        adminOnly: true,
+        hiddenOnRemote: true,
+    },
     // Automation
     {
         id: 'image-updates',