feat(web): P1 Vite skeleton beside Next — entry, router, guards, vitest 3

First increment of the approved Phase P RFC (webui-mission). Adds a Vite + React
Router SPA scaffold coexisting with the Next app: index.html with the theme
anti-flash script, src/main.tsx entry, the v1 parity route table under Guest/Auth
guard shells, and a dev proxy (/api, /socket.io ws) to the gateway on 14242 so the
SPA is same-origin in dev. vitest bumped to v3 (vite 8 pairing); existing specs
pass unchanged. Next remains the served app until the P5 cutover.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01ESFAnh2t9HmLwng8oW95St

apps/web/package.json

@@ -4,7 +4,9 @@
   "private": true,
   "scripts": {
     "build": "node ../../scripts/build-web.mjs",
+    "build:vite": "vite build",
     "dev": "next dev",
+    "dev:vite": "vite",
     "lint": "eslint src",
     "typecheck": "tsc --noEmit",
     "test": "vitest run --passWithNoTests",
@@ -19,6 +21,7 @@
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "react-markdown": "^10.1.0",
+    "react-router-dom": "^7.18.2",
     "socket.io-client": "^4.8.0",
     "tailwind-merge": "^3.5.0"
   },
@@ -28,9 +31,11 @@
     "@types/node": "^22.0.0",
     "@types/react": "^19.0.0",
     "@types/react-dom": "^19.0.0",
+    "@vitejs/plugin-react": "^6.0.5",
     "jsdom": "^29.0.0",
     "tailwindcss": "^4.0.0",
     "typescript": "^5.8.0",
-    "vitest": "^2.0.0"
+    "vite": "^8.2.1",
+    "vitest": "^3.2.7"
   }
 }