Function validate_config_file 

pub fn validate_config_file(
    path: &Path,
    content: &str,
) -> Result<Vec<String>, Vec<ConfigValidationError>>

Validate a config file and collect errors and warnings.

This validates:

• TOML syntax
• Type checking against UnifiedConfig schema
• Unknown keys with typo suggestions
• Deprecated keys (returns as warnings, not errors)

Returns Ok((warnings)) on success with optional deprecation warnings, or Err(errors) on validation failure.

Errors

Returns error if the operation fails.