Add Web Dashboard with multi-device control and callback hooks

Features:
- Web Dashboard: FastAPI-based dashboard with Vue.js frontend
  - Multi-device support (ADB, HDC, iOS)
  - Real-time WebSocket updates for task progress
  - Device management with status tracking
  - Task queue with execution controls (start/stop/re-execute)
  - Detailed task information display (thinking, actions, completion messages)
  - Screenshot viewing per device
  - LAN deployment support with configurable CORS

- Callback Hooks: Interrupt and modify task execution
  - step_callback: Called after each step with StepResult
  - before_action_callback: Called before executing action
  - Support for task interruption and dynamic task switching
  - Example scripts demonstrating callback usage

- Configuration: Environment-based configuration
  - .env file support for all settings
  - .env.example template with documentation
  - Model API configuration (base URL, model name, API key)
  - Dashboard configuration (host, port, CORS, device type)
  - Phone agent configuration (delays, max steps, language)

Technical improvements:
- Fixed forward reference issue with StepResult
- Added package exports for callback types and configs
- Enhanced dependencies with FastAPI, WebSocket support
- Thread-safe task execution with device locking
- Async WebSocket broadcasting from sync thread pool

Co-Authored-By: Claude <noreply@anthropic.com>

dashboard/dependencies.py

@@ -0,0 +1,39 @@
+"""
+Dependency injection for the dashboard.
+"""
+
+from typing import AsyncGenerator
+
+from dashboard.config import config
+from dashboard.services.device_manager import DeviceManager
+from dashboard.services.task_executor import TaskExecutor
+from dashboard.services.websocket_manager import WebSocketManager
+
+# Global service instances
+_device_manager: DeviceManager | None = None
+_task_executor: TaskExecutor | None = None
+_ws_manager: WebSocketManager | None = None
+
+
+def get_device_manager() -> DeviceManager:
+    """Get the device manager instance."""
+    global _device_manager
+    if _device_manager is None:
+        _device_manager = DeviceManager(device_type=config.DEFAULT_DEVICE_TYPE)
+    return _device_manager
+
+
+def get_task_executor() -> TaskExecutor:
+    """Get the task executor instance."""
+    global _task_executor
+    if _task_executor is None:
+        _task_executor = TaskExecutor(get_device_manager())
+    return _task_executor
+
+
+def get_ws_manager() -> WebSocketManager:
+    """Get the WebSocket manager instance."""
+    global _ws_manager
+    if _ws_manager is None:
+        _ws_manager = WebSocketManager()
+    return _ws_manager