Add interactive menu mode with ASCII art header

Summary

Add an interactive menu mode for sqlcmd with a visually appealing ASCII art header, similar to the Azure CLI's interactive experience.

Motivation

An interactive menu mode would:

• Improve discoverability: Help new users explore sqlcmd's features
• Reduce friction: Guide users through common tasks without memorizing flags
• Visual appeal: A branded ASCII art header creates a professional, memorable experience
• Consistency: Align with Azure CLI and other modern CLI tools that have interactive modes

Proposed Features

ASCII Art Header

   _____ ____    __    ________  _______
  / ___// __ \  / /   / ____/  |/  / __ \
  \__ \/ / / / / /   / /   / /|_/ / / / /
 ___/ / /_/ / / /___/ /___/ /  / / /_/ /
/____/\___\_\/_____/\____/_/  /_/_____/

Microsoft SQL Server Command Line Tool

(or similar branded design)

Interactive Menu Options

• Connect: Guided connection setup (server, auth method, database)
• Query: Enter and execute queries interactively
• Config: Manage contexts and endpoints (sqlcmd config commands)
• Containers: Start/stop/manage SQL containers
• Help: Browse commands and examples
• Recent: Show recent connections/queries

Navigation

• Arrow keys / number selection
• Fuzzy search for commands
• Breadcrumb navigation
• q or Esc to exit

Implementation Considerations

• Go TUI libraries: bubbletea, tview, promptui
• ASCII art generator or hand-crafted design
• Keyboard handling across platforms (Windows, Linux, macOS)
• Fallback for non-interactive terminals
• Integration with existing command structure

Inspiration

• Azure CLI interactive mode (az interactive)
• GitHub CLI (gh)
• lazygit, lazydocker
• k9s (Kubernetes TUI)

Tasks

• Design ASCII art header/logo
• Choose TUI library
• Design menu structure and navigation
• Implement main menu
• Add guided connection wizard
• Add interactive query mode
• Test on Windows, Linux, macOS terminals
• Document the interactive mode

Start by surveying sqlcmd’s existing command structure and entry point, then review how interactive modes work in Azure CLI and GitHub CLI. The issue calls for a TUI library, menu structure, guided connection and query flows, cross-platform keyboard handling, non-interactive fallback, tests, and documentation; done requires resolving those design choices and completing the listed tasks.