docs: Add guide for Claude Code to install Computer Use Demo

Added comprehensive installation guide written FROM the perspective of
Claude Code installing Computer Use Demo on the same system, rather than
the reverse scenario.

This is the correct use case: Claude Code (CLI-only tool) installs
Computer Use Demo to gain GUI/desktop control capabilities.

Key features:
- Step-by-step installation commands for Claude Code to execute
- Prerequisites verification and system dependency installation
- Python environment setup with virtual environment
- Systemd service configuration for auto-start
- Comprehensive troubleshooting and self-healing instructions
- Verification scripts to confirm successful installation
- Architecture diagram showing Claude Code + Computer Use working together
- Security considerations and best practices
- Usage guide for accessing the Streamlit UI (port 8501)

Use case: Claude Code can execute these commands to install Computer Use,
gaining screenshot, mouse click, and desktop navigation capabilities
beyond its current CLI-only limitations.

Note: This replaces the previous misunderstood scenario. The old
SETUP_VM_WITH_CLAUDE_CODE.md covers the reverse (Computer Use installing
Claude Code) which is kept for reference but is not the primary use case.

Author: claude