feat(network): add NetworkService for network availability monitoring

[CowboyGH]

🚀 Summary

Adds a NetworkService abstraction (and NetworkServiceImpl) to monitor network availability via connectivity_plus, with unit tests.

✨ Changes

• ✅ Added NetworkService API: init(), isConnected, connectionStream, hasNetwork().
• ✅ Implemented NetworkServiceImpl with cached state and deduplicated stream emissions.
• ✅ Registered the service in DI.
• ✅ Added Android permissions: ACCESS_NETWORK_STATE, INTERNET.
• ✅ Added unit tests for init, stream updates, deduplication, and dispose.

📱 iOS

• Updated Podfile.lock and project.pbxproj due to dependency version upgrades (Firebase/Firestore pods) and adding connectivity_plus.

🧪 Verification

• flutter analyze
• flutter test
• Built and launched on Android and iOS locally.