fix(nav): give the rail and the side panel a dead zone between them

The peek handlers sat on the rail's layout slot, which is 80px wide while the
card it holds is only 56px — so the card's own margin was a live hover zone with
nothing visible in it. Leaving the filter tab or panel to the left put the
cursor straight into it and the rail popped open unprompted; the gap between the
two hover zones was literally 0px. Moving the handlers onto the card leaves a
16px no man's land (x=69..85) where neither opens.

frontend/src/components/NavSidebar.tsx

@@ -275,11 +275,12 @@ export default function NavSidebar({
   return (
     // Layout slot: reserves only the slim footprint when unpinned, so the expanded rail (below)
     // overlays content instead of pushing it. Pinned reserves the full width (in-flow).
-    <div
-      {...peek.handlers}
-      className={`relative shrink-0 transition-[width] ${pinned ? "w-[232px]" : "w-20"}`}
-    >
+    <div className={`relative shrink-0 transition-[width] ${pinned ? "w-[232px]" : "w-20"}`}>
       <nav
+        // Peek handlers sit on the CARD, not the slot: the slot is wider than the card by its
+        // margin, and a hover zone out there would fire from the dead space next to the rail —
+        // leaving the side panel to the left would pop the rail open with nothing under the cursor.
+        {...peek.handlers}
         className={`glass absolute top-0 bottom-0 left-0 z-40 rounded-2xl flex flex-col py-3 m-3 transition-[width] ${
           slim ? "w-[56px] px-2" : "w-52 px-3"
         }`}