perf(*): bound list queries, batch fetches, harden media downloads

frontend/src/lib/components/policy/PolicyEditor.svelte

@@ -92,11 +92,11 @@
   });
 
   $effect(() => {
-    for (const policy of chatPolicies) {
-      if (policy.scope_id !== null) {
-        chats.ensure(policy.scope_id);
-      }
-    }
+    chats.ensureMany(
+      chatPolicies
+        .map((policy) => policy.scope_id)
+        .filter((id): id is number => id !== null)
+    );
   });
 
   function folderTitle(id: number | null): string {