feat(observability): phase 8 - container stats, notifications & dashboard

Add container monitoring and notification system:
- Docker Stats API: real-time CPU/memory for running containers
- Webhook notifications for errors (deploy failures, stale, proxy unhealthy)
- Event log auto-pruning (daily, 30-day retention)
- ContainerStats component with auto-polling progress bars
- SystemHealthCard dashboard widget with running/proxy/error counts
- Full EN/RU i18n for stats and system health

web/src/lib/components/InstanceCard.svelte

@@ -4,6 +4,7 @@
 <script lang="ts">
 	import type { Instance } from '$lib/types';
 	import StatusBadge from './StatusBadge.svelte';
+	import ContainerStats from './ContainerStats.svelte';
 	import ConfirmDialog from './ConfirmDialog.svelte';
 	import { IconPlay, IconStop, IconRestart, IconTrash, IconExternalLink } from '$lib/components/icons';
 	import { t } from '$lib/i18n';
@@ -141,6 +142,10 @@
 		</div>
 	</div>
 
+	{#if instance.status === 'running'}
+		<ContainerStats projectId={projectId} stageId={instance.stage_id} instanceId={instance.id} />
+	{/if}
+
 	{#if error}
 		<p class="mt-2 text-xs text-[var(--color-danger)]">{error}</p>
 	{/if}