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/load.go

@@ -120,7 +120,7 @@ func loadImage(ctx context.Context, run Runner, saved []byte, dryRun bool, say f
 	// Through a file rather than through stdin: the runner this repository shares runs a command
 	// and captures its output, and giving it a second mouth for one caller would change every
 	// applier's contract for the sake of one step (internal/apply's Runner).
-	tarball, err := os.CreateTemp("", "mesh-control-*.tar")
+	tarball, err := os.CreateTemp("", "mesh-controller-*.tar")
 	if err != nil {
 		return loaded, fmt.Errorf("nowhere to put the carried image while loading it: %w", err)
 	}