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

backend/src/__tests__/notification-matchers.test.ts

@@ -0,0 +1,89 @@
+import { describe, it, expect } from 'vitest';
+import {
+  matchesNotificationFilters,
+  ruleNeedsStackLabels,
+  appliesToBell,
+  appliesToExternal,
+} from '../helpers/notificationMatchers';
+import type { NotificationMatchContext } from '../helpers/notificationMatchers';
+
+const baseCtx: NotificationMatchContext = {
+  localNodeId: 1,
+  stackName: 'my-app',
+  category: 'monitor_alert',
+  level: 'error',
+  stackLabelIds: [10],
+};
+
+describe('notificationMatchers', () => {
+  it('matches when all non-empty filters pass', () => {
+    expect(matchesNotificationFilters(baseCtx, {
+      node_id: null,
+      stack_patterns: ['my-app'],
+      label_ids: [10],
+      categories: ['monitor_alert'],
+      levels: ['error'],
+    })).toBe(true);
+  });
+
+  it('rejects when node_id does not match', () => {
+    expect(matchesNotificationFilters(baseCtx, {
+      node_id: 2,
+      stack_patterns: [],
+      label_ids: null,
+      categories: null,
+    })).toBe(false);
+  });
+
+  it('rejects when stack pattern does not match', () => {
+    expect(matchesNotificationFilters(baseCtx, {
+      node_id: null,
+      stack_patterns: ['other'],
+      label_ids: null,
+      categories: null,
+    })).toBe(false);
+  });
+
+  it('rejects when category does not match', () => {
+    expect(matchesNotificationFilters(baseCtx, {
+      node_id: null,
+      stack_patterns: [],
+      label_ids: null,
+      categories: ['deploy_success'],
+    })).toBe(false);
+  });
+
+  it('rejects when level does not match', () => {
+    expect(matchesNotificationFilters(baseCtx, {
+      node_id: null,
+      stack_patterns: [],
+      label_ids: null,
+      categories: null,
+      levels: ['info'],
+    })).toBe(false);
+  });
+
+  it('matches any when all matchers empty', () => {
+    expect(matchesNotificationFilters(baseCtx, {
+      node_id: null,
+      stack_patterns: [],
+      label_ids: null,
+      categories: null,
+      levels: null,
+    })).toBe(true);
+  });
+
+  it('detects when stack labels are needed', () => {
+    expect(ruleNeedsStackLabels([{ node_id: null, stack_patterns: [], label_ids: [1], categories: null }])).toBe(true);
+    expect(ruleNeedsStackLabels([{ node_id: null, stack_patterns: [], label_ids: null, categories: null }])).toBe(false);
+  });
+
+  it('applies_to helpers', () => {
+    expect(appliesToBell('bell')).toBe(true);
+    expect(appliesToBell('external')).toBe(false);
+    expect(appliesToExternal('external')).toBe(true);
+    expect(appliesToExternal('bell')).toBe(false);
+    expect(appliesToBell('both')).toBe(true);
+    expect(appliesToExternal('both')).toBe(true);
+  });
+});