test: add Maestro end-to-end coverage

[ryanshepps]

Summary

Add end-to-end test coverage for IronLog using Maestro (https://github.com/mobile-dev-inc/Maestro) so core mobile flows are validated beyond unit tests and the static web build. Maestro is a good fit for this Expo/React Native app because it supports YAML UI flows across iOS and Android and can run against a built app on a simulator, emulator, or device.

Start with a small, stable smoke suite for the workflows most likely to regress in gym use: auth entry, opening the Log tab, adding/logging an exercise set, and verifying the logged workout is visible in History. The project currently has pnpm test, lint/type/build checks, and .github/workflows/pr-checks.yml; the new E2E path should fit that pnpm-first workflow and document any local simulator/emulator prerequisites.

Acceptance Criteria

• Can a developer run the Maestro smoke suite locally through a documented pnpm command?
• Do the initial flows cover at least one happy-path workout logging journey from app launch through history verification?
• Is the app configured with stable selectors or labels where needed so the Maestro flows are not brittle?
• Are CI or pre-merge expectations documented or wired so E2E coverage has a clear place in the release workflow?