fix(terminal): improve shell resolution with better error handling and ws proxy support

The `len(shell) <= 1` guard was too aggressive and provided no diagnostic info.
Now trims whitespace, resolves path in all cases, falls back to /bin/sh, and
logs detailed context for debugging. Also enable WebSocket proxying in Vite dev.

web/vite.config.js

@@ -13,6 +13,7 @@ export default defineConfig({
       '/api': {
         target: 'http://127.0.0.1:8095',
         changeOrigin: true,
+        ws: true,
       },
     },
   },