fix: Add missing 'standard' pytest marker to configuration

- Register 'standard' marker in pyproject.toml
- Resolves CI collection error in test_real_data_comprehensive.py
- Marker used for standard validation test categorization

Author: druvus

pyproject.toml

@@ -86,6 +86,7 @@ markers = [
     "property: Property-based tests using Hypothesis",
     "contract: API contract tests (interface validation)",
     "real_data: Real-world data validation tests",
+    "standard: Standard validation tests",
 
     # Speed markers (for CI optimization)
     "quick: Fast tests suitable for rapid feedback (<100ms)",