Expose Gradient via @ankhorage/zora/gradient so expo-linear-gradient stays optional

[artiphishle]

Problem

Gradient currently imports expo-linear-gradient directly:

import { LinearGradient } from 'expo-linear-gradient';

and ZORA also exports Gradient from the root package:

export { Gradient } from './components/gradient';

That means consumers that broadly import from @ankhorage/zora can cause the Gradient module graph to be evaluated, even when they do not intentionally use Gradient.

For native Expo consumers, this makes expo-linear-gradient effectively required even though it is declared as an optional peer dependency.

Desired direction

Make Gradient truly optional by moving the runtime/native dependency behind a dedicated subpath export:

import { Gradient } from '@ankhorage/zora/gradient';

The package root should avoid importing or re-exporting modules that require optional native dependencies.

Proposed design

1. Add an export subpath:

{
  "exports": {
    ".": { ... },
    "./gradient": {
      "react-native": "./src/components/gradient/index.ts",
      "browser": "./src/components/gradient/index.ts",
      "types": "./dist/components/gradient/index.d.ts",
      "import": "./dist/components/gradient/index.js",
      "default": "./dist/components/gradient/index.js"
    }
  }
}

2. Remove Gradient value export from root src/index.ts, or keep only type-level exports if TypeScript/build output can guarantee no runtime import.

3. Update docs/examples to import Gradient from:

import { Gradient } from '@ankhorage/zora/gradient';

4. Keep expo-linear-gradient as an optional peer dependency, but document that it is required for the @ankhorage/zora/gradient subpath.

5. Consider adding metadata for optional-native components so app generators can install native packages only when a manifest/component actually uses the component.

Acceptance criteria

• Importing from @ankhorage/zora root does not evaluate/import expo-linear-gradient.
• Gradient remains available from @ankhorage/zora/gradient.
• Apps that do not import/use Gradient do not need expo-linear-gradient installed.
• Apps that do import/use @ankhorage/zora/gradient get a clear peer dependency requirement.
• Typecheck/build/tests pass.

Notes

This is the architectural ZORA-side fix. The immediate generated-app unblock is tracked separately in ankhorage4, where generated apps should include expo-linear-gradient as long as root ZORA imports still make it effectively required.