Add production readiness validation suite

[Copilot]

Repository had no automated testing or validation infrastructure before production release.

Changes

Test Suite (21 tests)

• test_config.py - Configuration validation (URLs, timeouts, data sets 1-12, file extensions)
• test_csv_downloader.py - CSV loading, file categorization, error handling for malformed input
• test_scraper.py - Initialization, session headers, directory creation
• test_integration.py - End-to-end workflows (metadata collection, file organization)

Security

• CodeQL scan: 0 vulnerabilities

Documentation

• tests/README.md - Test suite documentation
• VALIDATION_REPORT.md - Validation results and coverage analysis
• Updated main README with testing section

Example

# All tests validate core functionality
python3 tests/run_tests.py

# CSV validation handles malformed data gracefully
with open('test.csv', 'w') as f:
    writer.writerow({'data_set': 'invalid', ...})  # Bad data_set
    
downloader.load_csv()  # Logs warning, skips bad row, continues

Test runner provides immediate feedback on all 21 tests with categorized results.

Original prompt

test and ensure its ready to ship

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