docs: add internal architecture documentation

[yedidyak]

Summary

• Add comprehensive architecture documentation for contributors and maintainers
• Create main ARCHITECTURE.md with high-level overview of Detox internals
• Add detailed subsection docs for client-server, devices, and artifacts systems

Changes

ARCHITECTURE.md

High-level overview covering:

• Realms pattern (Primary/Secondary contexts)
• DetoxWorker lifecycle
• Client-Server communication
• Device management
• Artifacts system
• Invocation system
• Test runner integration
• Key design patterns (Symbol-based privacy, Factory pattern, CAF, Event-driven architecture)

docs/architecture/client-server.md

• WebSocket protocol details
• Message format and actions table
• Connection lifecycle
• Synchronization and error handling

docs/architecture/devices.md

• Device allocation system (DeviceAllocator, DeviceRegistry)
• Runtime drivers hierarchy
• Platform-specific tools (AppleSimUtils, ADB)
• Device lifecycle flows

docs/architecture/artifacts.md

• ArtifactsManager plugin orchestration
• Plugin types (Screenshot, Video, Log, Instruments, UIHierarchy)
• Platform-specific implementations
• Path building and lifecycle hooks

Test plan

• Verify documentation renders correctly on GitHub
• Review accuracy of architecture diagrams
• Confirm all file paths referenced exist in the codebase

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