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/app.css

@@ -183,3 +183,29 @@ a:focus-visible {
 .font-mono {
 	font-family: var(--font-mono);
 }
+
+/* Card highlight for cross-entity navigation */
+@keyframes cardHighlight {
+	0%, 100% { box-shadow: none; }
+	25%, 75% { box-shadow: 0 0 0 3px var(--color-primary), 0 0 20px color-mix(in srgb, var(--color-primary) 30%, transparent); }
+}
+
+.card-highlight {
+	animation: cardHighlight 2s ease-in-out;
+	position: relative;
+	z-index: 11;
+}
+
+.nav-dim-overlay {
+	position: fixed;
+	inset: 0;
+	background: rgba(0, 0, 0, 0.4);
+	z-index: 10;
+	pointer-events: none;
+	opacity: 0;
+	transition: opacity 0.3s ease-in-out;
+}
+
+.nav-dim-overlay.active {
+	opacity: 1;
+}