feat(observability): phases 4-7 - complete frontend UI (big bang)

Add all frontend pages for observability & proxy management:
- Proxy Viewer: /proxies with grouped view, filtering, health indicators
- Proxy Creation: form with live validation, diagnostic hints, edit/delete
- Stale Containers: /containers/stale with dashboard widget, cleanup actions
- Event Log: /events with filters, pagination, real-time SSE streaming
- Navigation: proxies and events links in sidebar
- i18n: full EN/RU translations for all new features
- Settings: stale threshold configuration

web/src/lib/components/icons/IconProxies.svelte

@@ -0,0 +1,7 @@
+<script lang="ts">
+	interface Props { size?: number; class?: string; }
+	const { size = 20, class: c = '' }: Props = $props();
+</script>
+<svg xmlns="http://www.w3.org/2000/svg" width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" class={c} aria-hidden="true">
+	<circle cx="12" cy="12" r="10" /><path d="M12 2a14.5 14.5 0 0 0 0 20 14.5 14.5 0 0 0 0-20" /><path d="M2 12h20" />
+</svg>