Implement the three-column workbench frontend: resizable/collapsible nav with overshorthand collapse

Details (original message):
Implement the three-column workbench frontend: resizable/collapsible nav with overshorthand collapse, streaming chat with part renderers and process collapse, HITL choice cards with impact display and free-input pivot, plan/todos/artifacts/agents tabs, subagent tracker modal, schema-driven settings center with effect badges and masked secrets, profile management with import/export, plugin panel rendering, doc viewer with edit-save; contract shape tests.

vite.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+
+export default defineConfig({
+  plugins: [react()],
+  server: {
+    port: 5173,
+    proxy: {
+      '/api': { target: 'http://127.0.0.1:8787', changeOrigin: false },
+    },
+  },
+  test: { environment: 'node' },
+})