Add animated ASCII banner with rainbow wave effects to CLI

[Copilot]

This PR implements a colorful animated ASCII banner for the Scaffoldr CLI, similar to GitHub Copilot CLI's animated banner feature. The banner displays when users run any scaffoldr command and adds a delightful visual experience to the tool.

✨ Features Added

Animated ASCII Art Banner

• Professional "SCAFFOLDR" ASCII art logo
• Rainbow color cycling using HSL color space (360° hue spectrum)
• Sine wave animation effects that create flowing motion across the text
• Smooth 15 FPS animations running for 3 seconds
• Beautiful blue-to-purple gradient finale after animation completes

CLI Integration

• Seamlessly integrated with existing Typer CLI framework
• Shows by default on all commands for enhanced user experience
• --no-banner option to disable animations for CI/automation environments
• Graceful keyboard interrupt handling (Ctrl+C) with proper cleanup
• Fallback static banner for environments that don't support animations

Technical Implementation

• Built using Rich library for advanced terminal formatting
• Mathematical sine wave calculations for smooth animation effects
• HSL color space manipulation for vibrant rainbow transitions
• Proper cursor management and screen clearing
• Memory-efficient frame-based animation system

🧪 Quality Assurance

Added comprehensive test suite with 12 tests covering:

• Rainbow color generation and validation
• Wave effect application and frame differences
• CLI integration with and without banner
• Command-line argument parsing
• Error handling and edge cases

All code passes:

• ✅ Ruff linting and formatting
• ✅ MyPy type checking
• ✅ Pytest test suite (100% pass rate)

🚀 Usage Examples

# Show animated banner (default behavior)
scaffoldr generate my-project

# Skip animation for automation
scaffoldr --no-banner generate my-project --framework fastapi

# Version check (no banner shown)
scaffoldr --version

📖 Documentation

Updated README.md with:

• Feature description and capabilities
• Usage examples showing banner options
• Technical details about the animation system

The banner creates an engaging first impression while maintaining professional code quality and providing flexibility for different use cases.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• astral.sh
  • Triggering command: curl -LsSf REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>[FEATURE]</issue_title>
<issue_description>## Summary

Just want to add a feature for fun. I want something very similar to the GitHub Copilot CLI animation banner that was released recently. I wanted to a have a very similar colourful animation banner done in ASCII art.

Problem Statement

Doesn't solve any problem adds an interesting lower animation?

Affected Area

• Other (specify below)

Link: https://github.com/github/copilot-cli</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #86

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