Add Copilot instructions for repository standards and conventions

.github/copilot-instructions.md

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+# Copilot Instructions for CDAR PHP Library
+
+## Project Overview
+
+This is a PHP library for handling UN/EDIFACT D23B Cross Domain Acknowledgement and Response (CDAR) messages. Models are auto-generated from official UN/CEFACT XSD schemas.
+
+## Tech Stack
+
+- **Language**: PHP 8.3+
+- **Serialization**: JMS Serializer 3.32+
+- **Testing**: PHPUnit 12.5+
+- **Static Analysis**: PHPStan 2.1+ (max level)
+- **Code Style**: PHP-CS-Fixer 3.93+ with Symfony rules
+- **Refactoring**: Rector
+
+## Code Quality Standards
+
+### PHPStan Compliance
+- **CRITICAL**: All code MUST maintain 100% PHPStan compliance at maximum level
+- Run `vendor/bin/phpstan analyse` or `composer phpstan` before committing
+- No PHPStan errors are acceptable
+
+### Code Style
+- Follow Symfony coding standards enforced by PHP-CS-Fixer
+- Run `vendor/bin/php-cs-fixer fix` or `composer cs-fix` to auto-format code
+- Use `composer cs-check` to verify compliance without making changes
+- Configuration: `.php-cs-fixer.dist.php` with `@Symfony` rules
+
+### Type Safety
+- Use strict types declaration: `declare(strict_types=1);` in all PHP files
+- Always use type hints for parameters, return types, and properties
+- Prefer specific types over mixed types
+- Document complex types with PHPDoc when beneficial
+
+## Namespace and Autoloading
+
+- **Root namespace**: `TiimePDP\CrossDomainAcknowledgementAndResponse`
+- Follow PSR-4 autoloading standards
+- Source files in `src/` directory
+- Test files in `tests/` directory with `Tests` sub-namespace
+
+## Testing
+
+- Write PHPUnit tests for all new functionality
+- Run tests with `vendor/bin/phpunit` or `composer test`
+- Tests should be in `tests/` directory matching the `src/` structure
+- Configuration: `phpunit.xml`
+
+## Development Workflow
+
+### Quality Checks
+Run the complete quality check suite:
+```bash
+composer quality-check
+```
+
+This executes:
+1. Rector refactoring checks
+2. PHP-CS-Fixer style checks
+3. PHPStan static analysis
+4. PHPUnit tests
+
+### Individual Commands
+- **Rector**: `composer rector` or `./tools/bin/rector`
+- **CS Fix**: `composer cs-fix`
+- **CS Check**: `composer cs-check`
+- **PHPStan**: `composer phpstan`
+- **Tests**: `composer test`
+
+## License and Contributions
+
+- **License**: GPL-3.0-or-later
+- All modifications must be distributed under the same GPL-3.0-or-later license
+- Keep all comments and documentation in English
+- Ensure clear, descriptive commit messages
+
+## Key Architectural Patterns
+
+- Models represent UN/EDIFACT D23B standard structures
+- Use JMS Serializer for XML serialization/deserialization
+- Schema validation available via `SchemaValidator`
+- Models organized by:
+  - `Codelist`: Code list types
+  - `Enum`: Enumeration types
+  - `QualifiedDataType`: Qualified data types
+  - `UnqualifiedDataType`: Unqualified data types
+  - `ReusableAggregateBusinessInformationEntity`: Aggregate entities
+
+## Important Conventions
+
+1. **No Breaking Changes**: This is a library - maintain backward compatibility
+2. **Standard Compliance**: Follow UN/EDIFACT D23B specifications strictly
+3. **Minimal Dependencies**: Only add dependencies if absolutely necessary
+4. **Documentation**: Update README.md for user-facing changes
+5. **Performance**: Consider performance implications for large XML documents
+
+## Do Not
+
+- Do not lower PHPStan level or ignore PHPStan errors
+- Do not deviate from Symfony coding standards
+- Do not add code without proper type hints
+- Do not commit code that fails quality checks
+- Do not modify auto-generated model files without regenerating from XSD
+- Do not change the license terms