brokerd: ask_memory, a built-in memory tool that memoryd runs

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/brokerd/tests/memory_tools.rs

@@ -138,5 +138,5 @@ fn grant_files_cannot_name_the_memory_tools_or_take_a_built_in_id() {
         1,
         "the built-ins are not listed as the owner's"
     );
-    assert_eq!(with_shell.matchable().count(), 3);
+    assert_eq!(with_shell.matchable().count(), 4);
 }