Add CLAUDE.MD with testing and quality check instructions

CLAUDE.MD

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+# CLAUDE.MD - Instructions for AI Assistant
+
+This file contains important instructions for working on the phpdoc-parser project.
+
+## Testing and Quality Checks
+
+### Running Tests
+
+Tests are run using PHPUnit:
+```bash
+make tests
+```
+
+Or directly:
+```bash
+php vendor/bin/phpunit
+```
+
+### Running PHPStan
+
+PHPStan static analysis is run with:
+```bash
+make phpstan
+```
+
+Or directly:
+```bash
+php vendor/bin/phpstan
+```
+
+### Running All Checks
+
+To run all quality checks (lint, code style, tests, and PHPStan):
+```bash
+make check
+```
+
+This runs:
+- `lint` - PHP syntax checking with parallel-lint
+- `cs` - Code style checking with phpcs
+- `tests` - PHPUnit test suite
+- `phpstan` - Static analysis
+
+## CRITICAL RULES
+
+### ⚠️ MANDATORY: Run After Every Change
+
+**You MUST run both tests and PHPStan after every code change:**
+
+```bash
+make tests && make phpstan
+```
+
+Or use the comprehensive check:
+```bash
+make check
+```
+
+**DO NOT** commit or consider work complete until both tests and PHPStan pass successfully.
+
+### ⚠️ NEVER Delete Tests
+
+**NEVER delete any tests.** Tests are critical to the project's quality and regression prevention. If tests are failing:
+- Fix the implementation to make tests pass
+- Only modify tests if they contain actual bugs or if requirements have legitimately changed
+- When in doubt, ask before modifying any test
+
+## Other Available Commands
+
+- `make cs-fix` - Automatically fix code style issues
+- `make lint` - Check PHP syntax only
+- `make cs` - Check code style only
+- `make phpstan-generate-baseline` - Generate PHPStan baseline (use sparingly)
+
+## Workflow Summary
+
+1. Make code changes
+2. Run `make tests` - ensure all tests pass
+3. Run `make phpstan` - ensure static analysis passes
+4. Fix any issues found
+5. Commit only when both pass
+6. Repeat as needed
+
+**Remember: Tests and PHPStan MUST pass before any commit.**