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

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}")