feat(phase3): import/export, sparklines, user theme overrides

- JSON import/export with conflict resolution (skip/overwrite) + admin UI
- Ping history sparklines on AppWidget and AppCard (24h, 288 points)
- Hourly cleanup job for old AppStatus records
- User theme preferences (hue, saturation, mode, background, locale)
- Settings page with ThemeCustomizer (sliders, toggles, live preview)
- Prisma migration for user preference fields
- i18n translations for all new strings (EN/RU)

src/routes/admin/settings/+page.svelte

@@ -2,6 +2,7 @@
 	import { t } from 'svelte-i18n';
 	import type { PageData } from './$types.js';
 	import SettingsForm from '$lib/components/admin/SettingsForm.svelte';
+	import ImportExportPanel from '$lib/components/admin/ImportExportPanel.svelte';
 
 	let { data }: { data: PageData } = $props();
 </script>
@@ -10,11 +11,13 @@
 	<title>{$t('admin.system_settings')} — {$t('admin.panel')}</title>
 </svelte:head>
 
-<div>
+<div class="space-y-8">
 	<div class="mb-6">
 		<h1 class="text-2xl font-bold text-card-foreground">{$t('admin.system_settings')}</h1>
 		<p class="mt-1 text-sm text-muted-foreground">{$t('admin.settings_description')}</p>
 	</div>
 
 	<SettingsForm form={data.form} />
+
+	<ImportExportPanel />
 </div>