chore(ci): GitHub Actions — typecheck + iOS/macOS build

## Goal
Catch regressions on every PR and `develop` push.

## Acceptance criteria
- Workflow triggers on PR + push to `develop`
- TypeScript typecheck step
- iOS pod install + xcodebuild
- macOS pod install + xcodebuild
- Runs on macOS runner

## Notes
- macOS build step gated on #17 (macOS example app); iOS-only delivery first

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**Branch:** `chore/ci`
**PR:** #19