Serialized lazy-ref `src` values contain backslashes

Summary

On Windows OS, the fileRoutes() Vite plugin serializes lazy route refs with
backslashed src values (produced by node:path relative()), while Vite's
client manifest keys are always forward slashes. The two never match, so SSR
hydration preloads silently miss and SolidJS server lazy() breaks.

Steps to reproduce

1. On Windows, create a minimal app that actually runs the plugin through Vite:

   dummy-app/
   ├── package.json
   ├── vite.config.ts
   └── src/routes/index.tsx   ->  export default () => <h1>Home</h1>;
   

   // vite.config.ts
   import { fileRoutes } from "filesystem-routing/vite";
   import { defineConfig } from "vite";
   
   export default defineConfig({ plugins: [fileRoutes()] });
   

2. Build the client bundle:

   npx vite build
   

3. Inspect the emitted route manifest chunk (the module built from virtual:file-routes):

   "$component": {
     "src": "src\\routes\\index.tsx?pick=default&pick=$css&lang.tsx",  // <- backslashes
     ...
   }
   

4. Compare against Vite's client manifest keys (src/routes/index.tsx?..., always posix). No key matches, hydration preload misses, server lazy() never resolves.

Root cause

In src/vite/index.ts, both lazy-ref serializers emit:

src: relative(root, buildId)

node:path.relative() returns platform separators — backslashes on Windows.
Every other path in the pipeline is normalized to posix via normalizePath();
these two call sites were missed.

Start in src/vite/index.ts and inspect the two lazy-ref serializers that emit src with relative(root, buildId), comparing them with the pipeline's normalizePath() usage. Reproduce the plugin build on Windows and verify that the emitted route manifest uses forward-slash paths matching Vite's client manifest keys.