feat(mui): PageEnter kit primitive (consistent staggered page entrance) + adopt in WarehouseSuppliers

Each top-level child rises+fades in, staggered (0.4s, ease-out), so every page enters the same way and nothing appears instantly; honors prefers-reduced-motion. Replaces ad-hoc per-page motion.div entrance wrappers. One component → the look is tunable in one place.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/WarehouseSuppliers.tsx

@@ -1,5 +1,4 @@
 import { useState } from "react";
-import { motion } from "framer-motion";
 import Box from "@mui/material/Box";
 import Typography from "@mui/material/Typography";
 import IconButton from "@mui/material/IconButton";
@@ -24,6 +23,7 @@ import {
   TextField,
   StatusChip,
   PageHeader,
+  PageEnter,
   FilterBar,
   EmptyState,
   LoadingState,
@@ -344,22 +344,16 @@ export default function WarehouseSuppliers() {
   ];
 
   return (
-    <Box>
-      <motion.div
-        initial={{ opacity: 0, y: 12 }}
-        animate={{ opacity: 1, y: 0 }}
-        transition={{ duration: 0.25 }}
-      >
-        <PageHeader
-          title="Dodavatelé"
-          subtitle={subtitle}
-          actions={
-            <Button startIcon={PlusIcon} onClick={openCreateModal}>
-              Přidat dodavatele
-            </Button>
-          }
-        />
-      </motion.div>
+    <PageEnter>
+      <PageHeader
+        title="Dodavatelé"
+        subtitle={subtitle}
+        actions={
+          <Button startIcon={PlusIcon} onClick={openCreateModal}>
+            Přidat dodavatele
+          </Button>
+        }
+      />
 
       <FilterBar>
         <Box sx={{ flex: "1 1 320px" }}>
@@ -525,6 +519,6 @@ export default function WarehouseSuppliers() {
         confirmVariant="danger"
         loading={deleteMutation.isPending}
       />
-    </Box>
+    </PageEnter>
   );
 }