refactor: cleanup backend structure

cmd/go.mod

@@ -0,0 +1,3 @@
+module git.madunde.ad/madundead/obi/cmd
+
+go 1.25.3

cmd/obi.go

@@ -0,0 +1,5 @@
+package cmd
+
+func fooBar() {
+	fmt.Println!("foo")
+}