feat: add brownie skills

[hurali97]

Summary

This PR adds brownie Agent skills.

Test plan

Verified on a local brownfield setup - 🟢

Screen.Recording.2026-04-20.at.12.01.57.PM.mov

Agent references the brownie skill when prompted - 🟢

[Copilot]

Pull request overview

Adds a new brownie skill to the skills catalog, providing guided references for integrating and using @callstack/brownie across TypeScript, Android, and iOS in React Native brownfield apps.

Changes:

• Introduces skills/brownie/SKILL.md with routing to focused reference docs.
• Adds reference guides for getting started, schema/codegen, TypeScript usage patterns, Android integration, and iOS Swift + XCFramework packaging.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
skills/brownie/SKILL.md	Defines the new skill entrypoint and routes readers to the appropriate reference guides.
skills/brownie/references/getting-started.md	Getting-started checklist and end-to-end handoff steps across TS/iOS/Android.
skills/brownie/references/store-definition-and-codegen.md	Documents store schema authoring and brownfield codegen expectations.
skills/brownie/references/typescript-usage.md	Describes useStore selector patterns and low-level JS APIs (subscribe, getSnapshot, setState).
skills/brownie/references/android-usage.md	Documents Android registration and packaging/publish flow (incl. Gson requirement).
skills/brownie/references/swift-and-xcframework.md	Documents iOS store registration, SwiftUI/UIKit patterns, and XCFramework embedding flow.

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