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/link/messages.go

@@ -60,7 +60,7 @@ type Report struct {
 	// Carried are the machine's ports held by what this host raised from its own bundle.
 	//
 	// **So the mesh can assign around what it did not put here** (novox/hq ADR 0038). A node
-	// raises its substrate before any mesh exists, so the control plane has never heard of the
+	// raises its foundation before any mesh exists, so the control plane has never heard of the
 	// store or the broker — and would hand a module a port one of them holds, discovering it only
 	// when a container runtime refused to start.
 	//