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/ws_messages.py

@@ -0,0 +1,70 @@
+"""
+WebSocket message models for real-time updates.
+"""
+
+from datetime import datetime
+from enum import Enum
+from typing import Any, Dict, Optional
+
+from pydantic import BaseModel, Field
+
+
+class WSMessageType(str, Enum):
+    """WebSocket message types."""
+
+    DEVICE_UPDATE = "device_update"
+    TASK_STARTED = "task_started"
+    TASK_STEP = "task_step"
+    TASK_COMPLETED = "task_completed"
+    TASK_FAILED = "task_failed"
+    TASK_STOPPED = "task_stopped"
+    SCREENSHOT = "screenshot"
+    ERROR = "error"
+    PING = "ping"
+    PONG = "pong"
+
+
+class WSMessage(BaseModel):
+    """Base WebSocket message."""
+
+    type: WSMessageType = Field(..., description="Message type")
+    data: Dict[str, Any] = Field(default_factory=dict, description="Message data")
+    timestamp: datetime = Field(default_factory=datetime.now, description="Message timestamp")
+
+    class Config:
+        json_schema_extra = {
+            "example": {
+                "type": "task_step",
+                "data": {
+                    "task_id": "task_123",
+                    "device_id": "emulator-5554",
+                    "step": 5,
+                    "action": {"action": "Tap"},
+                    "thinking": "Tapping on button",
+                },
+                "timestamp": "2024-01-09T10:00:00",
+            }
+        }
+
+
+class StepUpdate(BaseModel):
+    """Step update message data."""
+
+    task_id: str = Field(..., description="Task ID")
+    device_id: str = Field(..., description="Device ID")
+    step: int = Field(..., description="Step number")
+    action: Optional[Dict[str, Any]] = Field(None, description="Action taken")
+    thinking: Optional[str] = Field(None, description="AI reasoning")
+    finished: bool = Field(False, description="Whether task is finished")
+    success: bool = Field(True, description="Whether step succeeded")
+    message: Optional[str] = Field(None, description="Status message")
+
+
+class ScreenshotUpdate(BaseModel):
+    """Screenshot update message data."""
+
+    device_id: str = Field(..., description="Device ID")
+    screenshot: str = Field(..., description="Base64 encoded screenshot")
+    width: int = Field(..., description="Screenshot width")
+    height: int = Field(..., description="Screenshot height")
+    timestamp: datetime = Field(default_factory=datetime.now)