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/inventory/ports.go

@@ -120,7 +120,7 @@ func (i *Inventory) assignPort(
 	if err != nil {
 		return Assigned{}, err
 	}
-	// And what the machine itself says it already holds — the substrate it raised before there
+	// And what the machine itself says it already holds — the foundation it raised before there
 	// was a mesh to ask (novox/hq ADR 0038). Not assignments: nothing here chose them, and
 	// nothing here can move them.
 	carried, err := i.carriedOn(ctx, nodeID)