fix(vite): proxy /plugin-ws WebSocket requests to the backend in dev (#757)

Plugin WebSocket connections (e.g. the official Terminal plugin) hang
in `npm run dev` because Vite proxies /api, /ws, and /shell but not
/plugin-ws/*. Production is unaffected because the same Express server
serves both the frontend and the WS gateway.

Co-authored-by: Haile <118998054+blackmammoth@users.noreply.github.com>

vite.config.js

@@ -37,6 +37,10 @@ export default defineConfig(({ mode }) => {
         '/shell': {
           target: `ws://${proxyHost}:${serverPort}`,
           ws: true
+        },
+        '/plugin-ws': {
+          target: `ws://${proxyHost}:${serverPort}`,
+          ws: true
         }
       }
     },