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/bootstrap/build_test.go

@@ -24,7 +24,7 @@ func TestAnInstallerWithNothingToBuildRefuses(t *testing.T) {
 
 // A repository without a commit refuses too, because a branch is somebody else's moving target.
 func TestABranchIsNotACommit(t *testing.T) {
-	err := Source{Repository: "https://example.invalid/mesh-control.git"}.Check()
+	err := Source{Repository: "https://example.invalid/mesh-controller.git"}.Check()
 	if err == nil {
 		t.Fatal("a source with no ref was accepted; genesis would have built whatever a branch pointed at")
 	}
@@ -35,7 +35,7 @@ func TestABranchIsNotACommit(t *testing.T) {
 
 // And a repository with a commit is enough.
 func TestARepositoryAndACommitIsEnough(t *testing.T) {
-	if err := (Source{Repository: "https://example.invalid/mesh-control.git", Ref: "a1b2c3d4"}).Check(); err != nil {
+	if err := (Source{Repository: "https://example.invalid/mesh-controller.git", Ref: "a1b2c3d4"}).Check(); err != nil {
 		t.Fatalf("a repository and a commit were refused: %v", err)
 	}
 }