fix(grid): prevent split collision by including source in overlap check

Server action: remove 'other.id === entryId' exclusion from the
split overlap scan so the source item's own footprint is treated
as occupied, forcing the split to find a different position.

UI: disable the split button via findEmptySpot check when no room
exists for the split stack, preventing a failed action.

src/app/(frontend)/logistics/structures/actions.ts

@@ -737,7 +737,7 @@ export async function splitGridStack(
 
         let overlaps = false;
         for (const other of existing) {
-          if (other.id === entryId || other.id == null) continue;
+          if (other.id == null) continue;
           const otherRes = other.resource as Resource;
           if (!otherRes || typeof otherRes === "number") continue;
           const otherRotated = other.rotated ?? false;

src/components/frontend/storage/GridToolbar.tsx

@@ -9,7 +9,7 @@ import {
   LayoutGridIcon,
   ListIcon,
 } from "lucide-react";
-import { GridItem, getItemFootprint, getGridOccupancy } from "@/lib/logistics";
+import { GridItem, getItemFootprint, getGridOccupancy, findEmptySpot } from "@/lib/logistics";
 import { Resource } from "@/payload-types";
 import { cn, pluralize } from "@/lib/utils";
 
@@ -41,6 +41,9 @@ export function GridToolbar({
   const occupancy = getGridOccupancy(storedResources, gridWidth, gridHeight);
   const res = selectedItem ? (selectedItem.resource as Resource) : null;
   const fp = res ? getItemFootprint(res, selectedItem!.rotated) : null;
+  const canSplit = selectedItem && res && fp
+    ? findEmptySpot(storedResources, fp.width, fp.height, gridWidth, gridHeight) !== null
+    : false;
 
   return (
     <div className="flex flex-col gap-3">
@@ -94,6 +97,7 @@ export function GridToolbar({
               <Button
                 variant="outline"
                 size="sm"
+                disabled={!canSplit}
                 onClick={() => onSplit(selectedItem.id, Math.floor(selectedItem.amount / 2))}
               >
                 <ScissorsIcon className="size-3.5" />

src/components/frontend/storage/StructureCard.tsx

@@ -46,7 +46,7 @@ export function StructureCard({ structure }: StructureCardProps) {
 
   return (
     <Link href={`/logistics/structures/${structure.id}`}>
-      <Item variant="outline" className="cursor-pointer group transition-all duration-200 hover:scale-[1.01] hover:[box-shadow:inset_0_2px_8px_rgba(255,255,255,0.12)]">
+      <Item variant="outline" className="cursor-pointer group transition-all duration-200 hover:scale-[1.01] hover:[box-shadow:inset_0_2px_8px_rgba(255,255,255,0.33)]">
         <ItemHeader>
           <div className="flex items-center gap-2">
             <ItemMedia variant="icon">