fix(web): build the compiler preset without mutating it, from the config dir

Two changes that npm's hoisting hid and pnpm's layout exposes:

- reactCompilerPreset()'s rolldown.filter is optional once @vitejs/plugin-react's
  optional type peers resolve (TS18048 on the in-place assignment). Spread the
  preset instead of mutating it.
- Babel resolves preset plugin names from process.cwd(). Builders that run Vite
  from the checkout root (installer, Docker, Nix) only found
  babel-plugin-react-compiler because npm hoisted it there. Pass the config
  dir as babel's cwd.

web/vite.config.ts

@@ -8,8 +8,13 @@ import react, { reactCompilerPreset } from "@vitejs/plugin-react";
  *  module — which made the babel pass parse the whole codebase. */
 function compilerPreset() {
   const preset = reactCompilerPreset();
-  preset.rolldown.filter.code = /\/>|<\/|from\s*['"][^'"]*react/;
-  return preset;
+  return {
+    ...preset,
+    rolldown: {
+      ...preset.rolldown,
+      filter: { ...preset.rolldown.filter, code: /\/>|<\/|from\s*['"][^'"]*react/ },
+    },
+  };
 }
 import tailwindcss from "@tailwindcss/vite";
 import path from "path";
@@ -84,7 +89,9 @@ export default defineConfig({
   },
   plugins: [
     react(),
-    babel({ presets: [compilerPreset()] }),
+    // Babel resolves the compiler preset's plugin from its cwd; builders run Vite from the
+    // checkout root, where only this workspace's node_modules has it.
+    babel({ cwd: configDir, presets: [compilerPreset()] }),
     tailwindcss(),
     hermesDevToken(),
   ],