tui: add /editor command to autocomplete for opening external editor

packages/opencode/src/cli/cmd/tui/component/prompt/autocomplete.tsx

@@ -255,6 +255,11 @@ export function Autocomplete(props: {
         description: "toggle theme",
         onSelect: () => command.trigger("theme.switch"),
       },
+      {
+        display: "/editor",
+        description: "open editor",
+        onSelect: () => command.trigger("prompt.editor"),
+      },
       {
         display: "/help",
         description: "show help",