Add comprehensive GitHub Copilot instructions for cpp-linter-hooks development

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides detailed guidance for GitHub Copilot coding agents working with the cpp-linter-hooks repository.

What's Included

The instructions cover all essential development workflows with validated commands and precise timing information:

🚀 Setup & Build Process

• Complete dependency installation steps (pip install .[dev] ~10s, clang tools ~2s)
• Build and test processes with explicit timeout warnings (test suite: 5.5 minutes - NEVER CANCEL)
• Python linting validation (ruff check ., ruff format --check .)

🧪 Testing & Validation

• Full test suite execution with coverage reporting
• Manual hook testing scenarios with working examples:

# Create malformed C++ file and test formatting
echo '#include <stdio.h>
int main() {for (;;) break; printf("Hello world!\n");return 0;}' > /tmp/test.c
clang-format-hook --version 21 --verbose /tmp/test.c

🛠 Hook Functionality

• Direct testing of clang-format-hook and clang-tidy-hook commands
• Workarounds for version checking issues and network timeouts in sandboxed environments
• Project structure navigation and key file locations

📋 Comprehensive Reference

• Repository structure with explanations of key directories (cpp_linter_hooks/, tests/, testing/)
• Entry points and command references
• Common troubleshooting scenarios
• CI/CD pipeline notes with timeout specifications

Validation

Every command, timing estimate, and workflow described in the instructions has been thoroughly tested and validated to ensure reliability. The instructions follow the imperative tone requirement and include explicit "NEVER CANCEL" warnings for long-running operations.

This provides coding agents with complete, accurate guidance to work effectively with the codebase from a fresh clone, eliminating the need for extensive exploration or trial-and-error approaches.

Fixes #110.

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.44%. Comparing base (d56ca2a) to head (b6c75c0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #111   +/-   ##
=======================================
  Coverage   94.44%   94.44%           
=======================================
  Files           3        3           
  Lines         108      108           
=======================================
  Hits          102      102           
  Misses          6        6           

☔ View full report in Codecov by Sentry.
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🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud