feat(hyperguild): brain query subcommand

Adds 'hyperguild brain query <topic>' against the brain HTTP REST
/query endpoint. Default human output prints path + score + title;
--json passes through the response envelope. --limit overrides the
default 5-result cap.

runBrainWrite remains a stub for Task 5.

cmd/hyperguild/main_test.go

@@ -35,8 +35,7 @@ func TestDispatch_UnknownSubcommand_ReturnsTwo(t *testing.T) {
 
 func TestDispatch_KnownSubcommand_RoutesAndReturnsExitCode(t *testing.T) {
 	var out, errBuf bytes.Buffer
-	code := dispatch(context.Background(), []string{"brain"}, strings.NewReader(""), &out, &errBuf)
-	// At this point, brain still returns the not-implemented error → exit 1.
+	code := dispatch(context.Background(), []string{"mode"}, strings.NewReader(""), &out, &errBuf)
 	assert.Equal(t, 1, code)
 	assert.Contains(t, errBuf.String(), "not implemented")
 }