fix: resolve CI linting and type errors

src/promptforge/core/exceptions.py

@@ -1,38 +1,49 @@
+"""Custom exceptions for PromptForge."""
+
+
 class PromptForgeError(Exception):
     """Base exception for PromptForge errors."""
+
     pass
 
 
 class InvalidPromptError(PromptForgeError):
     """Raised when a prompt YAML is malformed."""
+
     pass
 
 
 class ProviderError(PromptForgeError):
     """Raised when LLM API operations fail."""
+
     pass
 
 
 class ValidationError(PromptForgeError):
     """Raised when response validation fails."""
+
     pass
 
 
 class GitError(PromptForgeError):
     """Raised when git operations fail."""
+
     pass
 
 
 class RegistryError(PromptForgeError):
     """Raised when registry operations fail."""
+
     pass
 
 
 class MissingVariableError(PromptForgeError):
     """Raised when a required template variable is missing."""
+
     pass
 
 
 class ConfigurationError(PromptForgeError):
     """Raised when configuration is invalid."""
+
     pass