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/routes/proxies/[id]/edit/+page.svelte

@@ -0,0 +1,94 @@
+<!--
+  Phase 6: Edit Proxy page — loads a standalone proxy and wraps ProxyForm in edit mode.
+-->
+<script lang="ts">
+	import { page } from '$app/stores';
+	import { goto } from '$app/navigation';
+	import { onMount } from 'svelte';
+	import type { StandaloneProxy } from '$lib/types';
+	import { getProxy } from '$lib/api';
+	import { t } from '$lib/i18n';
+	import ProxyForm from '$lib/components/ProxyForm.svelte';
+	import { IconGlobe, IconLoader } from '$lib/components/icons';
+
+	let proxy: StandaloneProxy | null = $state(null);
+	let loading = $state(true);
+	let error = $state('');
+
+	const proxyId = $derived($page.params.id);
+
+	onMount(async () => {
+		try {
+			proxy = await getProxy(proxyId);
+		} catch (err: unknown) {
+			error = err instanceof Error ? err.message : 'Failed to load proxy';
+		} finally {
+			loading = false;
+		}
+	});
+
+	function handleSave(_proxy: StandaloneProxy): void {
+		goto('/proxies');
+	}
+
+	function handleDelete(_id: string): void {
+		goto('/proxies');
+	}
+
+	function handleCancel(): void {
+		goto('/proxies');
+	}
+</script>
+
+<svelte:head>
+	<title>{$t('proxies.form.editTitle')} - {$t('app.name')}</title>
+</svelte:head>
+
+<!-- Back link -->
+<div class="mb-6">
+	<a
+		href="/proxies"
+		class="inline-flex items-center gap-1 text-sm text-[var(--text-secondary)] hover:text-[var(--color-brand-600)] transition-colors"
+	>
+		<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+			<path d="M19 12H5" /><path d="m12 19-7-7 7-7" />
+		</svg>
+		{$t('common.back')}
+	</a>
+</div>
+
+<!-- Header -->
+<div class="mb-6 flex items-center gap-3">
+	<div class="flex h-10 w-10 items-center justify-center rounded-xl bg-[var(--color-brand-50)] text-[var(--color-brand-600)]">
+		<IconGlobe size={22} />
+	</div>
+	<h1 class="text-xl font-bold text-[var(--text-primary)]">{$t('proxies.form.editTitle')}</h1>
+</div>
+
+{#if loading}
+	<div class="flex items-center justify-center py-20">
+		<IconLoader size={24} class="text-[var(--color-brand-500)]" />
+		<span class="ml-2 text-sm text-[var(--text-secondary)]">{$t('common.loading')}</span>
+	</div>
+{:else if error}
+	<div class="rounded-xl border border-red-200 bg-red-50 p-6 text-center dark:border-red-900 dark:bg-red-950">
+		<p class="text-sm text-red-700 dark:text-red-300">{error}</p>
+		<a
+			href="/proxies"
+			class="mt-3 inline-block rounded-lg bg-red-600 px-4 py-2 text-sm font-medium text-white hover:bg-red-700 transition-colors"
+		>
+			{$t('common.back')}
+		</a>
+	</div>
+{:else if proxy}
+	<!-- Form card -->
+	<div class="mx-auto max-w-2xl rounded-2xl border border-[var(--border-primary)] bg-[var(--surface-card)] p-6 shadow-[var(--shadow-sm)]">
+		<ProxyForm
+			mode="edit"
+			{proxy}
+			onsave={handleSave}
+			ondelete={handleDelete}
+			oncancel={handleCancel}
+		/>
+	</div>
+{/if}