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

scenarios/audit-node.yml

@@ -1,6 +1,6 @@
 # One machine that becomes a mesh and then assigns itself the audit logger.
 #
-# The substrate is first-node's — a store, a broker, the control plane — and one module image on
+# The foundation is first-node's — a store, a broker, the control plane — and one module image on
 # top: the tool runtime carrying the audit-logger (mesh-catalog). The node enrols itself and the
 # mesh assigns it the audit logger, so its events account is one the mesh delivered, not the
 # broker's own (novox/hq ADR 0048).
@@ -20,7 +20,7 @@ machines:
     cpus: 2
 
 images:
-  - mesh-control:development
+  - mesh-controller:development
   # The tool runtime with the audit-logger, built by scripts/build-runtime-image.sh into the local
   # daemon and loaded onto the machine, which holds it by its own image ID.
   - mesh-runtime-audit:development