feat: add config file loading with error handling

Implement load_config() function with comprehensive error handling
- Loads and parses JSON config files
- Raises ConfigValidationError for missing files
- Raises ConfigValidationError for malformed JSON
- Includes 3 passing tests for all error cases

Test coverage:
- test_load_config_valid_json: Verifies successful JSON parsing
- test_load_config_file_not_found: Validates error on missing file
- test_load_config_invalid_json: Validates error on malformed JSON

tests/unit/test_config_merger.py

@@ -0,0 +1,37 @@
+import pytest
+import json
+import tempfile
+from pathlib import Path
+from tools.config_merger import load_config, ConfigValidationError
+
+
+def test_load_config_valid_json():
+    """Test loading a valid JSON config file"""
+    with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
+        json.dump({"key": "value"}, f)
+        temp_path = f.name
+
+    try:
+        result = load_config(temp_path)
+        assert result == {"key": "value"}
+    finally:
+        Path(temp_path).unlink()
+
+
+def test_load_config_file_not_found():
+    """Test loading non-existent config file"""
+    with pytest.raises(ConfigValidationError, match="not found"):
+        load_config("/nonexistent/path.json")
+
+
+def test_load_config_invalid_json():
+    """Test loading malformed JSON"""
+    with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
+        f.write("{invalid json")
+        temp_path = f.name
+
+    try:
+        with pytest.raises(ConfigValidationError, match="Invalid JSON"):
+            load_config(temp_path)
+    finally:
+        Path(temp_path).unlink()

tools/config_merger.py

@@ -0,0 +1,36 @@
+"""Configuration merging and validation for AI-Trader."""
+
+import json
+import sys
+from pathlib import Path
+from typing import Dict, Any, Optional
+
+
+class ConfigValidationError(Exception):
+    """Raised when config validation fails."""
+    pass
+
+
+def load_config(path: str) -> Dict[str, Any]:
+    """
+    Load and parse JSON config file.
+
+    Args:
+        path: Path to JSON config file
+
+    Returns:
+        Parsed config dictionary
+
+    Raises:
+        ConfigValidationError: If file not found or invalid JSON
+    """
+    config_path = Path(path)
+
+    if not config_path.exists():
+        raise ConfigValidationError(f"Config file not found: {path}")
+
+    try:
+        with open(config_path, 'r') as f:
+            return json.load(f)
+    except json.JSONDecodeError as e:
+        raise ConfigValidationError(f"Invalid JSON in {path}: {e}")