feat: card highlight system for cross-entity navigation

When clicking a CrossLink, the target entity ID is passed as
?highlight=<id> in the URL. The destination page:
1. Shows a semi-transparent dim overlay (z-index: 10)
2. Finds the card with data-entity-id matching the ID
3. Scrolls to it smoothly (block: center)
4. Applies a pulsing primary-color box-shadow animation (z-index: 11)
5. Cleans up overlay + animation after 2 seconds

If the card isn't in DOM yet (data still loading), a MutationObserver
waits up to 5 seconds for it to appear.

Changes:
- New highlight.ts utility with highlightFromUrl(), MutationObserver,
  dim overlay management
- Card component accepts entityId prop → data-entity-id attribute
- CrossLink accepts entityId prop → appends ?highlight=<id> to href
- All 9 entity pages: Card elements have entityId, highlightFromUrl()
  called after data loads
- CSS: cardHighlight keyframe animation + nav-dim-overlay styles

frontend/src/routes/notification-trackers/+page.svelte

@@ -16,6 +16,7 @@
 	import IconButton from '$lib/components/IconButton.svelte';
 	import CrossLink from '$lib/components/CrossLink.svelte';
 	import { snackSuccess, snackError } from '$lib/stores/snackbar.svelte';
+	import { highlightFromUrl } from '$lib/highlight';
 	import type { Tracker, ServiceProvider, NotificationTarget, TrackingConfig, TemplateConfig } from '$lib/types';
 
 	let loaded = $state(false);
@@ -69,7 +70,7 @@
 		} catch (err: any) {
 			loadError = err.message || 'Failed to load data';
 			snackError(loadError);
-		} finally { loaded = true; }
+		} finally { loaded = true; highlightFromUrl(); }
 	}
 	async function loadCollections() {
 		if (!form.provider_id) return;
@@ -370,7 +371,7 @@
 {:else if !showForm}
 	<div class="space-y-3 stagger-children">
 		{#each notificationTrackers as tracker}
-			<Card hover>
+			<Card hover entityId={tracker.id}>
 				<div class="flex items-center justify-between">
 					<div>
 						<div class="flex items-center gap-2">
@@ -379,7 +380,7 @@
 							<span class="text-xs px-1.5 py-0.5 rounded {tracker.enabled ? 'bg-[var(--color-success-bg)] text-[var(--color-success-fg)]' : 'bg-[var(--color-muted)] text-[var(--color-muted-foreground)]'}">
 								{tracker.enabled ? t('notificationTracker.active') : t('notificationTracker.paused')}
 							</span>
-t						<CrossLink href="/providers" icon="mdiServer" label={getProviderName(tracker.provider_id)} />
+t						<CrossLink href="/providers" icon="mdiServer" label={getProviderName(tracker.provider_id)} entityId={tracker.provider_id} />
 						</div>
 						<p class="text-sm text-[var(--color-muted-foreground)]">
 							{(tracker.collection_ids || []).length} {t('notificationTracker.albums_count')} · {t('notificationTracker.every')} {tracker.scan_interval}s · {(tracker.tracker_targets || []).length} {t('notificationTracker.linkedTargets')}