Add standalone web application and tag browser for git-artifact

[Copilot]

This PR implements a comprehensive standalone web application that provides a user-friendly interface for git-artifact commands and includes a visual tag browser for exploring repository relationships.

New Features

Standalone Web Application (git-artifact-app)

• Modern web interface with responsive design for desktop and mobile
• Form-based command execution for all git-artifact operations (init, clone, add-n-push, fetch-co, list, etc.)
• Real-time output display with terminal-style command feedback
• Input validation and error handling for required parameters
• Professional UI/UX with Font Awesome icons and modern styling

Interactive Tag Browser

• Visual graph representation of git-artifact's horizontal tag structure
• Interactive tag nodes - click any tag to view detailed information (commit, author, date, artifacts)
• Search and filtering capabilities for finding specific tags
• Multiple view modes (tree, graph, timeline) for different visualization needs
• Live demonstration of the horizontal commit model that makes git-artifact unique

Built-in Documentation

• Comprehensive help system integrated into the application
• Command reference with descriptions and usage examples
• Getting started guide for new users
• Concept explanations covering git-artifact's benefits and use cases

Technical Implementation

The application is built with:

• Pure HTML5, CSS3, and JavaScript (no external dependencies except Font Awesome icons)
• Python HTTP server for local development
• Responsive grid and flexbox layouts
• Modern ES6+ JavaScript with modular architecture

Usage

Start the application with:

./git-artifact-app

Then open http://localhost:8080 in your browser.

The interface provides three main tabs:

1. Commands - Execute git-artifact operations through intuitive forms
2. Tag Browser - Visualize and explore tag relationships
3. Help - Access comprehensive documentation and guides

Example Workflow

1. Use the "Initialize Repository" form to create a new git-artifact repo
2. Fill in your artifacts and use "Add & Push Artifact" with a version tag (e.g., v1.0)
3. Switch to the Tag Browser to see your artifacts visualized in the horizontal structure
4. Use "List Tags" or "Find Latest" to discover available artifacts

This implementation makes git-artifact accessible to users who prefer graphical interfaces while maintaining all the power and flexibility of the command-line tool. The tag browser particularly helps users understand the unique horizontal tagging approach that differentiates git-artifact from traditional git workflows.

Fixes #34.

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