feat: unified config file support for Expo

[artus9033]

Summary

This PR:

• brings standalone config file support to Expo & migrates the demo app setups to use it,
• modifies the signature of loadBrownfieldConfig to return null if it was not loaded

New config architecture:

Example behavior:

Scenario	Behavior
No config file, plugin props in app.json	Unchanged (current Expo workflow)
Config file only, plugins: ["@callstack/react-native-brownfield"]	New unified workflow
Config file + non-empty plugin props with overlap	Error, abort prebuild
Legacy frameworkName in app.json (no config file)	Still accepted
ios.scheme in config file	Drives both CLI package:ios and plugin frameworkName

Test plan

CI green - with migrated config in demo apps.

[Copilot]

Pull request overview

Adds unified Brownfield config-file support for Expo projects by centralizing config loading/merging in @callstack/brownfield-cli and updating the Expo config plugin + docs accordingly.

Changes:

• Introduces @callstack/brownfield-cli/expo-plugin-config utilities for Expo prebuild (load config, detect overlap with app.json plugin props, resolve effective plugin config).
• Updates config loading to return null when no config source exists and expands CLI types/schema/docs with Expo-specific nested keys (android.expo.*, ios.expo.*) and richer descriptions.
• Migrates the Expo demo app to register the plugin without app.json options when using a config file.

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
yarn.lock	Updates Rock toolchain deps and adds Prettier lock entries.
packages/react-native-brownfield/src/expo-config-plugin/withBrownfield.ts	Switches Expo plugin config resolution to the new CLI-provided resolver + overlap guard.
packages/cli/src/types.ts	Adds Expo nested config types and tweaks iOS flag typing used for schema generation.
packages/cli/src/expoPluginConfig.ts	New shared Expo plugin config resolution utilities (overlap detection + resolution).
packages/cli/src/config.ts	Exposes config filenames/constants; loadBrownfieldConfig now returns null when no source exists.
packages/cli/src/brownie/config.ts	Adjusts Brownie config lookup for nullable loadBrownfieldConfig.
packages/cli/src/tests/expoPluginConfig.test.ts	Adds tests for Expo plugin config resolution utilities.
packages/cli/src/tests/config.test.ts	Updates tests for loadBrownfieldConfig nullable behavior.
packages/cli/schema.json	Extends schema with Expo nested keys and adds/updates descriptions.
packages/cli/package.json	Exposes new ./expo-plugin-config entrypoint; bumps Rock deps; adds Prettier for schema formatting.
docs/docs/docs/getting-started/expo.mdx	Recommends config-file-driven setup; clarifies plugin options usage rules.
docs/docs/docs/cli/brownfield.mdx	Updates CLI docs to match current iOS options.
docs/docs/docs/api-reference/configuration.mdx	Documents Expo projects config rules + Expo-only nested keys and example.
apps/ExpoApp54/app.json	Migrates plugin registration to string-only (no tuple options).
apps/AppleApp/package.json	Bumps @rock-js/tools version.
.changeset/young-snails-lose.md	Changeset for schema/description generation updates.
.changeset/nine-mice-fall.md	Changeset for unified Expo config support across packages.

Comments suppressed due to low confidence (1)

docs/docs/docs/api-reference/configuration.mdx:85

• The config loader expects brownfield.config.js (see CONFIG_BASE_NAME = "brownfield"), but the docs here mention react-native-brownfield.config.js. This is inconsistent with the earlier “Expo projects” section and with the actual filenames supported by loadBrownfieldConfig.

## JavaScript config file

If you prefer a JavaScript file, create `react-native-brownfield.config.js` and export a plain object with `module.exports`:

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