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/ValidationChecklist.svelte

@@ -0,0 +1,73 @@
+<!--
+  Phase 6: Validation checklist for proxy destination validation.
+  Shows each validation step with pass/fail/pending status indicators.
+-->
+<script lang="ts">
+	import type { ValidationResult } from '$lib/types';
+	import { IconCheck, IconX, IconLoader } from '$lib/components/icons';
+	import { t } from '$lib/i18n';
+
+	interface Props {
+		result: ValidationResult | null;
+		loading?: boolean;
+	}
+
+	const { result, loading = false }: Props = $props();
+
+	/** Map step names to i18n keys. */
+	const stepLabelKeys: Record<string, string> = {
+		syntax: 'proxies.validation.syntax',
+		dns: 'proxies.validation.dns',
+		tcp: 'proxies.validation.tcp',
+		http: 'proxies.validation.http'
+	};
+
+	function getStepLabel(name: string): string {
+		const key = stepLabelKeys[name];
+		return key ? $t(key) : name;
+	}
+</script>
+
+{#if loading || result}
+	<div class="rounded-lg border border-[var(--border-primary)] bg-[var(--surface-card)] p-4">
+		<h4 class="text-sm font-medium text-[var(--text-primary)] mb-3">
+			{$t('proxies.validation.title')}
+		</h4>
+
+		{#if loading && !result}
+			<div class="flex items-center gap-2 text-sm text-[var(--text-secondary)]">
+				<IconLoader size={16} />
+				<span>{$t('proxies.validation.checking')}</span>
+			</div>
+		{:else if result}
+			<ul class="space-y-2">
+				{#each result.steps as step}
+					<li>
+						<div class="flex items-center gap-2">
+							{#if step.passed}
+								<span class="flex h-5 w-5 flex-shrink-0 items-center justify-center rounded-full bg-emerald-100 dark:bg-emerald-950">
+									<IconCheck size={14} class="text-emerald-600 dark:text-emerald-400" />
+								</span>
+								<span class="text-sm text-[var(--text-primary)]">{getStepLabel(step.name)}</span>
+								{#if step.message}
+									<span class="text-xs text-[var(--text-tertiary)]">&mdash; {step.message}</span>
+								{/if}
+							{:else}
+								<span class="flex h-5 w-5 flex-shrink-0 items-center justify-center rounded-full bg-red-100 dark:bg-red-950">
+									<IconX size={14} class="text-red-600 dark:text-red-400" />
+								</span>
+								<span class="text-sm text-[var(--text-primary)]">{getStepLabel(step.name)}</span>
+								{#if step.message}
+									<span class="text-xs text-[var(--text-tertiary)]">&mdash; {step.message}</span>
+								{/if}
+							{/if}
+						</div>
+						{#if !step.passed && step.hint}
+							<p class="ml-7 mt-1 text-xs text-amber-600 dark:text-amber-400">{step.hint}</p>
+						{/if}
+					</li>
+				{/each}
+			</ul>
+		{/if}
+	</div>
+{/if}