Add Reflux state management and cross-platform demo

[MelbourneDeveloper]

TLDR;

New reflux package for Redux-style state management + demo showing shared state between Flutter and React web.

What Does This Do?

• Adds reflux: Redux-inspired state management using Dart's sealed classes for type-safe action handling
• Adds reflux_demo: Counter app demonstrating shared state logic between Flutter and React web
• Adds markdown_editor: Example web app showcasing dart_node_react capabilities
• Updates dart_node_react with improved hooks and JSX DSL
• Updates dart_node_ws with proper test infrastructure
• Restructures CI into tiered publish workflows

Brief Details

New Packages:

• reflux: Store, reducers, middleware, selectors with full pattern matching on sealed action classes
• examples/reflux_demo/counter_state: Shared state logic (actions, reducer, selectors)
• examples/reflux_demo/flutter_counter: Flutter app consuming shared state
• examples/reflux_demo/web_counter: React web app consuming same shared state
• examples/markdown_editor: Full-featured markdown editor with live preview

Key improvements:

• State as typedef records (structural typing)
• Actions as sealed classes with exhaustive pattern matching
• Memoized selectors via createSelector1/2/3
• No string-based action types - all type-safe

How Do The Tests Prove The Change Works?

• reflux: Full test coverage for store, middleware, selectors, enhancers, compose
• flutter_counter: Widget tests with golden image comparisons
• web_counter: Browser-based UI integration tests
• markdown_editor: Browser-based component tests
• dart_node_react: Split monolithic test file into focused test modules