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/models/__init__.py

@@ -0,0 +1,37 @@
+"""
+Data models for the dashboard API.
+
+Includes Pydantic schemas for devices, tasks, and WebSocket messages.
+"""
+
+from dashboard.models.device import (
+    DeviceType,
+    DeviceStatus,
+    DeviceSchema,
+    DeviceInfo,
+)
+from dashboard.models.task import (
+    TaskStatus,
+    TaskRequest,
+    TaskSchema,
+    TaskCreateRequest,
+)
+from dashboard.models.ws_messages import (
+    WSMessageType,
+    WSMessage,
+    StepUpdate,
+)
+
+__all__ = [
+    "DeviceType",
+    "DeviceStatus",
+    "DeviceSchema",
+    "DeviceInfo",
+    "TaskStatus",
+    "TaskRequest",
+    "TaskSchema",
+    "TaskCreateRequest",
+    "WSMessageType",
+    "WSMessage",
+    "StepUpdate",
+]