Significantly enhance .github/copilot-instructions.md with comprehensive development guidance

[Copilot]

This PR transforms the GitHub Copilot instructions from a basic guide into a comprehensive development resource for Git AI contributors and Copilot users.

What's Enhanced

🐛 Debugging & Troubleshooting

Added extensive debugging section with real debug output examples showing the actual Git AI hook session format:

=== GIT AI HOOK DEBUG SESSION ===
📋 INITIALIZATION
📝 GIT DIFF PROCESSING  
🤖 AI PROCESSING
📊 ANALYSIS RESULTS

Includes environment setup (RUST_LOG=debug), common issues/solutions, and testing scenarios for edge cases like Unicode content, binary files, and large diffs.

🧪 Testing Documentation

Enhanced with real test examples from the codebase:

#[test]
fn test_parse_diff_with_c_i_prefixes() {
    let diff = r#"diff --git a/src/config.rs b/src/config.rs..."#;
    let files = parse_diff(diff).unwrap();
    assert_eq!(files[0].operation, "modified");
}

Documents all 11 comprehensive test categories matching ./scripts/comprehensive-tests and integration test patterns.

🤖 AI Provider Integration

Added detailed integration examples with real code from the codebase:

• OpenAI integration (src/openai.rs) with structured function calling
• Ollama integration (src/ollama.rs) for local models
• Model-specific optimizations with token limits and context lengths
• JSON schema definitions for function tools

⚡ Performance & Development Workflow

• Justfile commands documentation (just local-install, just integration-test)
• Script utilities covering Fish shell scripts in ./scripts/ directory
• Token management strategies with smart truncation and prioritization
• Parallel processing patterns using both rayon and tokio

📊 Reference Tables

Added quick-reference tables for:

Model	Use Case	Speed	Quality	Cost
gpt-4.1	Default, balanced	Medium	High	Medium
gpt-4o	Best quality	Slow	Highest	High
gpt-4o-mini	Fast iteration	Fast	Good	Low

🔧 Enhanced CLI Documentation

Expanded configuration reference with all available keys, defaults, and examples:

git-ai config set max-tokens 512          # Control API usage
git-ai config set max-commit-length 72    # Limit message length

Code Quality

All improvements use real examples from the actual codebase (src/multi_step_analysis.rs, tests/function_calling_test.rs, etc.) ensuring accuracy and maintainability. The documentation now serves as both a comprehensive reference and practical development guide while maintaining consistency with existing patterns.

Tests pass and code compiles without warnings, ensuring no functionality is broken.

Original prompt

Improve .github/copilot-instructions.md

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[Copilot]

Pull Request Overview

This PR significantly enhances the GitHub Copilot instructions document from a basic guide into a comprehensive development resource. The enhancement adds extensive debugging documentation with real examples, comprehensive testing patterns from the actual codebase, AI provider integration details, and performance optimization strategies.

Key Changes:

• Debugging & troubleshooting section with real debug output examples and environment setup
• Real test examples extracted from the actual codebase (tests/function_calling_test.rs, src/multi_step_integration.rs, etc.)
• AI provider integration documentation covering OpenAI and Ollama with actual code patterns
• Performance optimization strategies including token management, model selection guidelines, and fallback implementations

Comments suppressed due to low confidence (2)

.github/copilot-instructions.md:1

• The model version gpt-4.1 does not exist in OpenAI's model lineup. This should likely be gpt-4-turbo or another valid OpenAI model identifier.

# GitHub Copilot Instructions for Git AI

.github/copilot-instructions.md:1

• The configuration example uses gpt-4.1 which is not a valid OpenAI model. This should be updated to use a valid model identifier like gpt-4-turbo.

# GitHub Copilot Instructions for Git AI

[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 5 comments.