fix(demo): build client plugin bundles before serving dsh web

demo:web and the README Web UI instructions ran only build:web (the Vite
frontend shell), never the root build that emits each web-client plugin's
lib/client.js. On a clean checkout every /plugins/<id>/client.js 404s and
the client loader shows "Failed to load plugins".

Run pnpm run build before build:web in both the demo:web script and the
README instructions for the installed ~/.dsh/source checkout.

package.json

@@ -94,7 +94,7 @@
     "demo:code-mode": "node scripts/demo-code-mode.mjs",
     "demo:cordis": "node --expose-internals --import tsx packages/examples/tui-demo/src/bin.ts examples/cordis-agent/cordis.yml",
     "demo:acp": "node --import tsx packages/examples/acp-demo/src/bin.ts --config examples/acp-agent/cordis.yml",
-    "demo:web": "npm run build:web && node --import tsx apps/cli/src/bin.ts web",
+    "demo:web": "npm run build && npm run build:web && node --import tsx apps/cli/src/bin.ts web",
     "postinstall": "node scripts/install-lefthook.mjs"
   },
   "devDependencies": {