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/bundle/bundle.go

@@ -27,13 +27,13 @@ import (
 // nothing and reporting success — a host that silently did nothing on a first node would look
 // exactly like one that worked.
 //
-//go:embed substrate-arch.lock
+//go:embed foundation-arch.lock
 var archLock []byte
 
-//go:embed substrate-alpine.lock
+//go:embed foundation-alpine.lock
 var alpineLock []byte
 
-//go:embed substrate-android.lock
+//go:embed foundation-android.lock
 var androidLock []byte
 
 var locks = map[string][]byte{
@@ -52,7 +52,7 @@ func Raw(system string) []byte { return locks[system] }
 
 // IsEmpty reports whether anything was built in. A bundle of only comments and whitespace is
 // empty for this purpose: a placeholder is a comment, and treating it as content would mean a
-// host claims to carry a substrate it does not.
+// host claims to carry a foundation it does not.
 func IsEmpty(system string) bool {
 	for _, line := range strings.Split(string(locks[system]), "\n") {
 		line = strings.TrimSpace(line)