Write Android migration guide to Jetpack Compose

[anshu7vyas]

This commit introduces a detailed migration strategy document for transforming the Stocked! app from a legacy 2018 codebase to a modern Android application using the latest architecture and libraries.

Key additions:

• ANDROID_MIGRATION_GUIDE.md: 80+ page comprehensive migration plan covering all phases from foundation setup to production deployment
• docs/README.md: Quick reference guide for developers

Migration highlights:

• Transform from Java to Kotlin
• Replace XML layouts with Jetpack Compose
• Implement MVI architecture pattern
• Migrate SQLite to Room database
• Add Hilt dependency injection
• Implement Coroutines and Flow for reactive programming
• Material 3 design system
• Comprehensive testing strategy

The guide includes:
✓ Current state analysis (1,870 lines of Java code audited) ✓ Target architecture with modern Android stack
✓ 5 detailed migration phases (10-14 week timeline) ✓ Production-ready code examples for all components ✓ Testing strategies (unit, integration, UI, E2E)
✓ Risk management and rollback plans
✓ Success metrics and KPIs

Each phase includes:

• Clear deliverables and timelines
• Detailed implementation steps
• Code examples with best practices
• Testing requirements
• Risk mitigation strategies

Tech stack covered:

• Jetpack Compose with Material 3
• MVI (Model-View-Intent) architecture
• Room Database with Flow
• Hilt Dependency Injection
• Kotlin Coroutines & StateFlow
• WorkManager for background tasks
• DataStore for preferences
• Comprehensive testing (JUnit, MockK, Turbine)

This serves as the architectural blueprint for the complete modernization of the application.