fix(web): add @vitejs/plugin-react — dev mode needs the React Refresh runtime

TanStack Start's dev server requires a React Refresh plugin; without it `/@react-refresh`
404s, the client entry 500s, and nothing hydrates (blank screen — the production build was
unaffected since rollup handles JSX there). Pinned to the v4 line: plugin-react 6 imports
`vite/internal` (Vite 7 only) and we're on Vite 6. Must sit after tanstackStart() in the
plugin list.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/vite.config.ts

@@ -1,5 +1,6 @@
 import { defineConfig } from 'vite'
 import { tanstackStart } from '@tanstack/react-start/plugin/vite'
+import viteReact from '@vitejs/plugin-react'
 import viteTsConfigPaths from 'vite-tsconfig-paths'
 import tailwindcss from '@tailwindcss/vite'
 import { paraglideVitePlugin } from '@inlang/paraglide-js'
@@ -28,5 +29,8 @@ export default defineConfig({
       // fetching against a token-gated local API), still on the TanStack Start runtime.
       spa: { enabled: true },
     }),
+    // Must come AFTER tanstackStart — provides the React JSX transform + Refresh runtime
+    // that Start's dev mode requires (omitting it leaves the client JS unable to load).
+    viteReact(),
   ],
 })