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/system/android.go

@@ -35,7 +35,7 @@ import (
 // while disconnected, reconcile already happens on start, and the mesh already reports *last
 // heard from* rather than alarming on silence.
 //
-// It also **cannot be the first node** — every step of raising a substrate is a shape it
+// It also **cannot be the first node** — every step of raising a foundation is a shape it
 // refuses — and its bundle says so rather than being an empty placeholder.
 type android struct{}