feat: add mobile package publishing via GitHub Packages

- Add release.yml workflow for iOS/Android builds and publishing
- Create Package.swift for Swift Package Manager distribution
- Add Sources/CooklangFind re-export module
- Bump version to 0.5.1

On tag push, the workflow:
- Builds iOS XCFramework (arm64 device + simulator)
- Builds Android AAR (arm64-v8a, armeabi-v7a, x86_64)
- Creates GitHub Release with artifacts
- Updates Package.swift with binary checksum
- Publishes Android to GitHub Packages Maven

Author: dubadub