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/protocol.go

@@ -88,7 +88,7 @@ type Report struct {
 
 	// Carried are the machine's ports held by what that host raised from its own bundle.
 	//
-	// **The half the mesh cannot know** (novox/hq ADR 0038). The substrate is not a module — a
+	// **The half the mesh cannot know** (novox/hq ADR 0038). The foundation is not a module — a
 	// node raises it before any mesh exists — so without being told, the mesh assigns a module a
 	// port the store or the broker already holds, and hears about it from a container runtime.
 	//