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/providers/+page.svelte

@@ -13,6 +13,7 @@
 	import ConfirmModal from '$lib/components/ConfirmModal.svelte';
 	import IconButton from '$lib/components/IconButton.svelte';
 	import { snackSuccess, snackError } from '$lib/stores/snackbar.svelte';
+	import { highlightFromUrl } from '$lib/highlight';
 	import type { ServiceProvider } from '$lib/types';
 
 	let providers = $derived(providersCache.items);
@@ -34,7 +35,7 @@
 			loadError = '';
 		} catch (err: any) {
 			loadError = err.message || t('providers.loadError');
-		} finally { loaded = true; }
+		} finally { loaded = true; highlightFromUrl(); }
 		// Ping all providers in background
 		for (const p of providers) {
 			health = { ...health, [p.id]: null };
@@ -151,7 +152,7 @@
 {:else}
 	<div class="space-y-3 stagger-children">
 		{#each providers as provider}
-			<Card hover>
+			<Card hover entityId={provider.id}>
 				<div class="flex items-center justify-between">
 					<div class="flex items-center gap-3">
 						<div class="health-dot {health[provider.id] === true ? 'online' : health[provider.id] === false ? 'offline' : 'checking'}"></div>