Add unit tests for channel utilities and configure testing environment

- Created a new test file `channels.test.ts` to cover utilities related to channel configurations and targets.
- Implemented tests for normalizing and grouping selected channels by type, as well as building channel targets from account data and cron history.
- Mocked necessary dependencies to isolate tests and ensure accurate results.
- Updated `vite.config.ts` to set up the testing environment with jsdom and enable global variables for tests.

electron/gateway/diagnostics.ts

@@ -0,0 +1,40 @@
+import type { ChannelAccountCatalogGroup, ChannelConnectionStatus } from '@src/lib/channel-types';
+import { buildChannelStatusSummary, type ChannelStatusSummary } from '@electron/utils/channel-status';
+
+export interface GatewayHealthSnapshot {
+  ok: boolean;
+  status: 'connected' | 'disconnected' | 'reconnecting';
+  initialized: boolean;
+  mode: 'in-process';
+}
+
+export interface GatewayDiagnosticsSummary {
+  status: ChannelConnectionStatus;
+  gateway: GatewayHealthSnapshot;
+  channels: ChannelStatusSummary;
+}
+
+function normalizeGatewayStatus(status: GatewayHealthSnapshot['status']): ChannelConnectionStatus {
+  if (status === 'reconnecting') return 'connecting';
+  return status;
+}
+
+export function buildGatewayDiagnosticsSummary(
+  health: GatewayHealthSnapshot,
+  channelGroups: readonly ChannelAccountCatalogGroup[],
+): GatewayDiagnosticsSummary {
+  const channels = buildChannelStatusSummary(channelGroups);
+  const gatewayStatus = normalizeGatewayStatus(health.status);
+
+  return {
+    status: health.ok
+      ? (channels.status === 'connected'
+        ? 'connected'
+        : channels.status === 'disconnected'
+          ? 'degraded'
+          : channels.status)
+      : gatewayStatus,
+    gateway: health,
+    channels,
+  };
+}