fix: Add next/compat/router shim

[wobsoriano]

Adds a new compat-router shim for next/compat/router, the public Next.js API intended for components shared between Pages Router and App Router.

@clerk/nextjs (ref) import from next/compat/router. The next/compat/router package entry is CJS (module.exports = require(...)), which Vite cannot extract named ESM exports from — causing a "does not provide an export named 'useRouter'" error at runtime. Adding a native ESM shim in vinext resolves this without requiring apps to add a resolve.alias workaround.

Temporary fix:

// vite.config.ts

resolve: {
  alias: {
    // next/compat/router ships a CJS entry; alias to the ESM version instead.
    "next/compat/router": resolve("./node_modules/next/dist/esm/client/compat/router.js"),
  },
},

Locally tested via pnpm link