feat: add React-free ./model entry point

[mfal]

Why

Model definitions only need GhostMakerModel and getModelName, and both are
free of React. The main entry, however, pulls in react, react/jsx-runtime and
@tanstack/react-query as soon as it is imported. Any package that defines
models therefore depends on React, even when it never renders anything — for
example a framework-agnostic domain-model package meant to run in Node or a CLI.

What

• New subpath @mittwald/react-ghostmaker/model, built like ./polytype.
  It exports GhostMakerModel, ghostMakerModel, getModelName, getModelId
  and the types GhostMakerModelMeta and DynamicModel. It shares the model
  registry with the main entry, so models defined through ./model resolve in
  React ghosts as before.
• react and @tanstack/react-query are now optional peers. Only the main
  entry needs them, and anyone using it has React installed anyway. The version
  ranges are unchanged.
• getModelName and getModelId moved from queries.ts to metaData.ts.
  queries.ts carries a type import from types.ts, which references React
  types; left there, model.d.ts would require @types/react in consumers
  compiling with skipLibCheck: false. queries.ts re-exports them, so the main
  entry is unchanged.
• GhostMakerModelMeta and DynamicModel are now exported from the main
  entry too, so it keeps offering everything ./model does.
• README: a section on when to import from ./model, and a note that React
  and TanStack Query are only required for the main entry.

Keeping it React-free

reactFreeEntries.test.ts walks the import graph of model.ts and
polytype.ts statically, type imports and export … from included, and fails
as soon as it reaches react, react/*, react-dom or
@tanstack/react-query. A self-test asserts that the walker does find React
behind the main entry, so it cannot pass vacuously.

Compatibility

Purely additive. The main entry's runtime exports and their signatures are
identical before and after (compared on the build output); the only additions
are the two type exports. Suggested release: 1.6.0.

Verification

• pnpm test in the package: tsc, eslint, build, vitest (25/25), license check.
• dist/esm/model.js loads only metaData.js and @sindresorhus/is;
  dist/types/model.d.ts only references type-fest.
• Installed the packed tarball into an empty project without React: npm installs
  neither peer, ./model runs (decorator, getModelName, getModelId), and
  tsc --skipLibCheck false compiles a file using the decorator and
  GhostMakerModelMeta.

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