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/two-nodes.yml

@@ -17,7 +17,7 @@ machines:
     at: { segment: hosting, address: [192.0.2.10] }
     egress: true
     inbound: allow
-    # The whole substrate, the registry, the builder, an adopted workload and the modules under
+    # The whole foundation, the registry, the builder, an adopted workload and the modules under
     # test all land here — eleven containers before the forge arrives. At the 1GiB default this
     # machine thrashes, and it presents as "the mesh hangs": every exec slows from 15s to 105s
     # and the forge test fails on a status poll that is merely queued behind page-outs.
@@ -30,7 +30,7 @@ machines:
     memory: 2GiB
 
 images:
-  - mesh-control:development
+  - mesh-controller:development
   # And the builder, because it is a module the mesh assigns rather than a program somebody
   # starts by hand — which is the only way its credential can be one the mesh delivered.
   - mesh-builder:development