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

internal/store/store_test.go

@@ -136,7 +136,7 @@ func TestNothingIsAnOrphanWhenEverythingIsDeclared(t *testing.T) {
 }
 
 func TestADeclarationDoesNotOrphanWhatTheBundleRaised(t *testing.T) {
-	// 04-ISSUES/010. A first node raises its substrate from the bundle it carries, then enrols
+	// 04-ISSUES/010. A first node raises its foundation from the bundle it carries, then enrols
 	// and is sent a declaration naming two resources. Before origins, that removed the store, the
 	// broker and the control plane that had sent it — the mesh deleting itself over the link the
 	// message arrived on, in under a second, on the first end-to-end run.
@@ -175,7 +175,7 @@ func TestTheBundleDoesNotOrphanWhatTheMeshDeclared(t *testing.T) {
 func TestStateWrittenBeforeOriginsExistedIsTreatedAsCarried(t *testing.T) {
 	// Every resource a host had applied before this field existed came from its bundle, because
 	// there was no other way to tell it anything. Guessing the other way would have the first
-	// declaration remove the substrate — which is the fault this exists to prevent, arriving
+	// declaration remove the foundation — which is the fault this exists to prevent, arriving
 	// through the upgrade that fixes it.
 	s := State{Resources: []Applied{{ID: "store", Type: "container", Target: "mesh-store"}}}