Highlight active and current snapshots in sidebar

Add white left border for the swapped-to snapshot and green left border
for the auto-saved "you were here" snapshot, matching timeline markers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

js/snapshot_manager.js

@@ -1582,6 +1582,14 @@ const CSS = `
 .snap-item-node {
     border-left: 3px solid #6d28d9;
 }
+.snap-item-active {
+    background: rgba(255,255,255,0.06);
+    border-left: 3px solid #fff;
+}
+.snap-item-current {
+    background: rgba(16,185,129,0.06);
+    border-left: 3px solid #10b981;
+}
 .snap-node-badge {
     display: inline-block;
     font-size: 9px;
@@ -2387,6 +2395,12 @@ async function buildSidebar(el) {
             if (diffBaseSnapshot && diffBaseSnapshot.id === rec.id) {
                 item.classList.add("snap-diff-base");
             }
+            if (rec.id === activeSnapshotId) {
+                item.classList.add("snap-item-active");
+            }
+            if (rec.id === currentSnapshotId) {
+                item.classList.add("snap-item-current");
+            }
 
             const info = document.createElement("div");
             info.className = "snap-item-info";