feat(ra-data-simple-prisma): add /server subpath export to keep react-admin out of server bundles

[dan2811]

Hi, I was having an issue with a project that uses this package and I've had to resolve temporarily, using resolutions in my package.json. Have used claude to raise this PR which fixes my issue. Would be great if you could consider merging.

Disclaimer: I haven't looked in-depth at this code and I'm not familiar with this repo, so please review carefully! Hopefully it's not just AI slop!

Summary

ra-data-simple-prisma exposes both a client-side dataProvider (used
by react-admin in the browser) and server-side request handlers (used
inside Next.js API routes to talk to Prisma directly) from a single
bundle. That bundle has a top-level import { HttpError } from 'react-admin'
which is only used by the client dataProvider, but because it sits at
the top of dist/index.js / dist/index.mjs, any server-side import
of a handler transitively pulls in react-admin, ra-core,
ra-ui-materialui, and react-router-dom at runtime.

On Vercel / Next.js this causes two real problems:

1. The serverless function bundle is bloated with UI-only packages it
   never executes.
2. ESM resolution can break the deployment. With react-router-dom@7.x
   the package's exports field causes Next.js NFT (file tracer) to
   include dist/index.js (CJS) while Node ESM resolution at runtime
   picks dist/index.mjs — the missing .mjs is then never traced and
   the function crashes with MODULE_NOT_FOUND in production.

Fix

Split into two entry points via subpath exports:

Entry	Contents	Pulls in react-admin?
ra-data-simple-prisma	dataProvider + handlers (back-compat)	yes (unchanged)
ra-data-simple-prisma/server	handlers + helpers only	no

Server-side consumers can switch to:

import { defaultHandler } from "ra-data-simple-prisma/server";

and react-admin (plus its transitive UI deps) disappears from the
function's traced files entirely.

Changes

• New src/server.ts entry that re-exports only the server APIs.
• Http.ts, audit/types.ts, audit/auditHandler.ts now use
  import type for their react-admin imports — these were already
  type-only usages, but the explicit type keyword guarantees esbuild
  erases them at build time so the server bundle has no require('react-admin').
• package.json:
  • exports map for . (back-compat) and ./server with .d.ts,
    ESM, and CJS targets for each.
  • tsup now builds both entries.
  • react-admin moved to peerDependenciesMeta.optional = true so
    server-only consumers don't get install warnings.
  • New build:check script that asserts the server bundle has no
    react-admin reference.
• tests/serverBundle.test.ts — Jest guard that fails CI if dist/server.{js,mjs}
  ever start referencing react-admin again.
• README documents the new /server subpath.
• Changeset (minor bump).

Non-breaking

The top-level entry is unchanged: it still re-exports both the
dataProvider and the handlers, so existing imports continue to work
without modification.

Test plan

• pnpm build produces dist/index.{js,mjs,d.ts} and dist/server.{js,mjs,d.ts}
• grep react-admin dist/server.* returns nothing
• pnpm test passes (164/164, including the new serverBundle.test.ts)
• pnpm build:check passes
• Manual: import from "ra-data-simple-prisma/server" in a Next.js
  App Router function on Vercel, confirm the function bundle no
  longer traces react-admin / react-router-dom