feat(tools): add computer tool for GUI automation via cua-computer-server

Add a new `computer` tool that enables agents to control desktop GUIs:
- Take screenshots
- Click, double-click, right-click at coordinates
- Type text, press keys, hotkey combinations
- Scroll in any direction
- Move cursor, drag operations
- Get screen size and cursor position

Integrates with cua-computer-server which can run in:
- Sandbox mode (cua-xfce, cua-ubuntu Docker images)
- Node mode (Linux with supervisor setup)

Includes setup documentation and example screenshot.

docs/guides/computer-server-setup.md

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+# Computer-Server Setup for GUI Automation
+
+This guide explains how to set up [cua-computer-server](https://github.com/trycua/cua/tree/main/libs/python/computer-server) for desktop GUI automation with Clawdbot agents.
+
+## Overview
+
+The `computer` tool enables agents to:
+- Take screenshots of the desktop
+- Click at screen coordinates
+- Type text and press keys
+- Scroll and drag
+- Control native applications
+
+## Setup Options
+
+### Option 1: Sandbox Mode (Recommended)
+
+Use Cua's pre-built desktop sandbox images. Computer-server is already installed and running.
+
+![cua-xfce desktop sandbox](./cua-xfce-screenshot.png)
+
+```yaml
+# In your clawdbot config
+agents:
+  defaults:
+    sandbox:
+      docker:
+        image: ghcr.io/trycua/cua-xfce:latest
+```
+
+Available sandbox images:
+
+| Image | Description |
+|-------|-------------|
+| `ghcr.io/trycua/cua-xfce:latest` | Linux + XFCE desktop |
+| `ghcr.io/trycua/cua-ubuntu:latest` | Linux + Kasm desktop |
+
+For more options including Windows and Android, see [Cua Desktop Sandboxes](https://cua.ai/docs/cua/guide/get-started/what-is-desktop-sandbox#docker-sandboxes).
+
+### Option 2: Node Mode (Linux)
+
+For Linux nodes, you can set up computer-server to run as a daemon using supervisor.
+
+#### 1. Install computer-server
+
+```bash
+pip install cua-computer-server
+```
+
+#### 2. Create startup script
+
+Create `/usr/local/bin/start-computer-server.sh`:
+
+```bash
+#!/bin/bash
+set -e
+
+# Wait for X server to be ready
+echo "Waiting for X server to start..."
+while ! xdpyinfo -display :0 >/dev/null 2>&1; do
+    sleep 1
+done
+echo "X server is ready"
+
+# Start computer-server
+export DISPLAY=:0
+python3 -m computer_server --port 8000
+```
+
+Make it executable:
+
+```bash
+chmod +x /usr/local/bin/start-computer-server.sh
+```
+
+#### 3. Configure supervisor
+
+Create `/etc/supervisor/conf.d/computer-server.conf`:
+
+```ini
+[program:computer-server]
+command=/usr/local/bin/start-computer-server.sh
+user=<your-user>
+autorestart=true
+stdout_logfile=/var/log/computer-server.log
+stderr_logfile=/var/log/computer-server.error.log
+```
+
+#### 4. Start the service
+
+```bash
+sudo supervisorctl reread
+sudo supervisorctl update
+sudo supervisorctl start computer-server
+```
+
+### Option 3: Node Mode (Windows/macOS)
+
+**TBD** - Setup instructions for Windows and macOS nodes will be added in a future update.
+
+## Usage
+
+Once computer-server is running, agents can use the `computer` tool:
+
+```
+Use the computer tool to take a screenshot and then click on the "File" menu.
+```
+
+The agent will:
+1. Call `computer` with `action: "screenshot"` to see the screen
+2. Identify the coordinates of "File" menu
+3. Call `computer` with `action: "click"` and the coordinates
+
+## Configuration
+
+You can configure the computer-server URL in your Clawdbot config:
+
+```yaml
+tools:
+  computer:
+    serverUrl: "http://localhost:8000"
+```
+
+Or per-agent:
+
+```yaml
+agents:
+  my-agent:
+    tools:
+      computer:
+        serverUrl: "http://192.168.1.100:8000"
+```
+
+## MCP Alternative
+
+Computer-server also exposes an MCP (Model Context Protocol) interface at `/mcp`. This could be used as an alternative integration method if Clawdbot adds MCP client support in the future.
+
+To use computer-server as a standalone MCP server:
+
+```bash
+python -m computer_server --mcp
+```
+
+## Troubleshooting
+
+### Connection refused
+
+Ensure computer-server is running and accessible:
+
+```bash
+curl http://localhost:8000/status
+```
+
+Should return: `{"status": "ok", "os_type": "...", "features": [...]}`
+
+### No display
+
+If computer-server fails with display errors, ensure:
+- X server is running (Linux)
+- The `DISPLAY` environment variable is set correctly
+- The user has permission to access the display
+
+### Sandbox not connecting
+
+Ensure the sandbox container has port 8000 exposed and the network is accessible from Clawdbot.
+
+## Security Considerations
+
+- **Sandbox mode**: Isolated container - safe for untrusted workloads
+- **Node mode**: Controls the actual device screen - use only with trusted agents
+- **Gateway mode**: Not supported - would give agents control of your actual desktop
+
+## Related
+
+- [cua-computer-server](https://github.com/trycua/cua/tree/main/libs/python/computer-server) - Desktop automation server
+- [Cua Desktop Sandboxes](https://cua.ai/docs/cua/guide/get-started/what-is-desktop-sandbox) - Pre-built sandbox images