feat: Add MCP Prompts for common home lab workflows

- Added 8 pre-configured prompts for common tasks:
  • security_audit - Comprehensive security check
  • health_check - Quick system health overview
  • troubleshoot_container - Docker container debugging
  • performance_analysis - System performance review
  • network_audit - Network security and config review
  • plan_stack_deployment - Docker Compose deployment planning
  • investigate_high_usage - Resource usage troubleshooting
  • backup_planning - Backup and disaster recovery

- Prompts combine multiple tools into complete workflows
- Compatible with Claude Desktop, VS Code Copilot, and MCP SDKs
- Documented in docs/prompts.md with usage examples
- Updated README to highlight prompts feature

Prompts follow MCP specification 2025-06-18 and leverage
FastMCP's @mcp.prompt decorator for seamless integration.

Each prompt provides structured, step-by-step guidance for
the AI assistant to complete complex multi-tool operations.

Author: mdlmarkham