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>

phone_agent/__init__.py

@@ -5,8 +5,14 @@ This package provides tools for automating Android and iOS phone interactions
 using AI models for visual understanding and decision making.
 """
 
-from phone_agent.agent import PhoneAgent
-from phone_agent.agent_ios import IOSPhoneAgent
+from phone_agent.agent import AgentConfig, PhoneAgent, StepResult
+from phone_agent.agent_ios import IOSAgentConfig, IOSPhoneAgent
 
 __version__ = "0.1.0"
-__all__ = ["PhoneAgent", "IOSPhoneAgent"]
+__all__ = [
+    "PhoneAgent",
+    "IOSPhoneAgent",
+    "AgentConfig",
+    "IOSAgentConfig",
+    "StepResult",
+]