feat(memory): add opt-in scoped memory tools

FIXME.md

@@ -13,6 +13,9 @@
 - [ ] Provider-backed workflows (agent delegation and actual skill invocation)
   have not been tested; they require configured credentials and explicit
   approval of any model usage.
+- [ ] Optional memory has deterministic tests but has not been checked for
+  persistence and isolation across restarts in a live OpenCode 2.0.24 profile.
+  Provider-backed learning proposals are not implemented.
 - [ ] Global/XDG installation is not implemented; project-level update and
   uninstall are supported, while global installation remains out of scope.
 - [ ] The package name and GitHub URL are provisional and must be confirmed