fix: refine signal popover hover behavior

web/app.js

@@ -155,6 +155,7 @@ let recordings = [];
 let recordingsFetchInFlight = false;
 let showDebugOverlay = localStorage.getItem('spectre.debugOverlay') !== '0';
 let hoveredSignal = null;
+let popoverHideTimer = null;
 
 const GAIN_MAX = 60;
 const timelineWindowMs = 5 * 60 * 1000;
@@ -1293,7 +1294,7 @@ window.addEventListener('mousemove', (ev) => {
     hoveredSignal = hoverHit.signal;
     renderSignalPopover(hoverHit, hoverHit.signal);
   } else {
-    hideSignalPopover();
+    scheduleHideSignalPopover();
   }
   if (isDraggingSpectrum) {
     const dx = ev.clientX - dragStartX;

web/style.css

@@ -217,9 +217,9 @@ canvas { display: block; width: 100%; height: 100%; border-radius: var(--r-sm);
   position: absolute; z-index: 8; pointer-events: none; min-width: 180px; max-width: 220px;
   padding: 10px 12px; border-radius: 10px; border: 1px solid var(--line-hi);
   background: rgba(6, 10, 18, 0.94); box-shadow: 0 18px 50px rgba(0,0,0,0.38);
-  font-size: 0.72rem; color: var(--text); display: none;
+  font-size: 0.72rem; color: var(--text); display: none; opacity: 0; transform: translateY(4px);
 }
-.signal-popover.open { display: block; }
+.signal-popover.open { display: block; opacity: 1; transform: translateY(0); transition: opacity 90ms ease, transform 90ms ease; }
 .signal-popover__title { font-family: var(--mono); font-weight: 700; margin-bottom: 4px; color: var(--accent); }
 .signal-popover__meta { color: var(--text-mute); margin-bottom: 6px; }
 .signal-popover__scores { display: grid; gap: 4px; }