fix: replace CSS keyframe highlight with direct style pulse for reliability

CSS animation was interfering with stagger animation on cards.
Now uses setInterval-based box-shadow pulse with computed primary
color from CSS variables. Pulses glow on/off every 400ms for 2.5s,
then fades out via transition.

frontend/src/app.css

@@ -184,12 +184,7 @@ a:focus-visible {
 	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 dim overlay for cross-entity navigation */
 .nav-dim-overlay {
 	position: fixed;
 	inset: 0;