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/apply/apply_test.go

@@ -459,7 +459,7 @@ func TestForgettingAUnitThatIsGoneDoesNotStrandTheNode(t *testing.T) {
 	}
 }
 
-// --- package, container and action (novox/hq 07-the-substrate.md, ADR 0006, ADR 0005) ---
+// --- package, container and action (novox/hq 07-the-foundation.md, ADR 0006, ADR 0005) ---
 
 func parseTrusted(t *testing.T, raw string) *declaration.Declaration {
 	t.Helper()