feat: UI layer implementation & real-time WebSocket architecture

[Thixq]

🚀 UI Layer Implementation & Real-Time WebSocket Architecture

Summary

This PR introduces the complete UI layer (Home & Coin Detail screens) with a high-performance real-time data pipeline powered by WebSocket streams, background isolate parsing, and smart state management via Provider.

---

🏗️ Architecture Overview

┌──────────────┐     ┌──────────────┐     ┌───────────────────────┐
│   HomeView   │◄────│HomeViewModel │◄────│    MarketManager      │
│ CoinDetail   │     │  (Provider)  │     │  (REST + WebSocket)   │
└──────────────┘     └──────────────┘     └───────┬───────────────┘
                                                  │
                                    ┌─────────────┴─────────────┐
                                    │                           │
                              ┌─────▼──────┐          ┌────────▼────────┐
                              │ DioService │          │WebSocketService │
                              │ (Snapshot) │          │  (Real-time)    │
                              └────────────┘          └────────┬────────┘
                                                               │
                                                    ┌──────────▼──────────┐
                                                    │ IsolateParser       │
                                                    │ (Background JSON)   │
                                                    └─────────────────────┘

---

✨ Features & Changes

🖥️ UI Layer (New)

• HomeView — Filterable coin list with real-time price updates, search bar with debounce, keyboard-aware scrolling
• SmartCoinRow — Self-updating row widget that subscribes directly to MarketManager.getCoinStream() for its symbol, avoiding parent-level rebuilds
• CoinDetailView — Scrollable detail page with price section, 24h stats grid, and volume cards
• HomeViewModel — Provider-based state management with loading → loaded → disconnected → error lifecycle

⚡ Performance Optimizations

• Isolate-based JSON parsing — WebSocketIsolateParser processes incoming WebSocket messages on a background isolate with incremental char-by-char JSON scanning
• Throttled UI updates — MarketManager batches price updates every 1000ms to avoid excessive widget rebuilds
• Selective notifications — HomeViewModel.notifyListeners() only fires on snapshot emissions or state transitions, not on every price tick
• RepaintBoundary on list items to isolate repaint regions
• distinct() on coin streams using Equatable comparison

🔌 WebSocket & Connectivity

• Constructor-injected parser — WebSocketService now requires parser and manuellyRetry via constructor (removes runtime setParser())
• Manual retry support — When manuellyRetry: true, auto-reconnect is disabled; user triggers reconnect explicitly
• Socket status stream — MarketManager.socketStatusStream exposes connection state (connected, disconnected, reconnecting)
• Disconnect detection — HomeViewModel listens to socket status and shows a "Connection Lost" dialog with retry action
• Heartbeat mechanism — 5s inactivity timeout assumes dead connection and triggers reconnect

🏛️ Dependency Injection

• DependencyContainer — Centralized GetIt configuration with readOrCreate<T>() for lazy singleton registration
• DependencyInstances — Clean API to access services (dioService, webSocketService<T>()) and managers (marketManager)

🧪 Tests

• WebSocketIsolateParser tests — Comprehensive tests covering single object, array, large batch, and error scenarios
• Updated WebSocketService tests — Adapted to constructor-based parser injection
• Updated MarketManager tests — Mock regeneration and useIsolate parameter stubs

---

📁 Files Changed (19 files)

Category	Files
New — Views	home_view.dart, home_view_model.dart, smart_coin_row.dart, coin_detail_view.dart, coin_detail_view_model.dart, detail_card.dart, detail_grid.dart, price_section.dart
New — Services	websocket_isolate_parser.dart
New — DI	dependency_container.dart, dependency_instances.dart
Modified — Core	market_manager.dart, web_socket_service.dart, main.dart
Modified — Tests	market_manager_test.dart, market_manager_test.mocks.dart, web_socket_service_test.dart
New — Tests	websocket_isolate_parser_test.dart
Config	devtools_options.yaml

Stats: +1449 / -264 across 19 files

---

🔍 How to Test

1. flutter pub get
2. flutter run — Home screen loads coin list via REST snapshot, then live prices stream via WebSocket
3. Search "BTC" or "TRY" in the search bar
4. Tap any coin to open the detail page
5. Kill network to observe "Connection Lost" dialog → tap Retry
6. flutter test — All unit tests pass