Rename mesh-control -> mesh-controller, substrate -> foundation

One name per thing, per the HQ glossary: the module/container/image/binary/repo
becomes mesh-controller, the seat the-controller, and the store+broker pair the
foundation (embedded base bundles, default template and example lock renamed with
their go:embed directives). No behaviour change — a pure vocabulary rename.

Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx

src/messaging/index.ts

@@ -9,7 +9,7 @@ export type { Envelope, EventHeaders };
 
 /** A request/reply call and a publish/subscribe surface over the mesh broker. */
 export interface Broker {
-  /** Ask one question and await one answer — the client side; the shape mesh-control's command
+  /** Ask one question and await one answer — the client side; the shape mesh-controller's command
    *  API is reached by. */
   request<Req, Res>(key: string, body: Req): Promise<Res>;
   /** Answer a question — the server side of request/reply. A tool runtime serves invocations this