Use custom SeedPassError instead of sys.exit

src/seedpass/errors.py

@@ -1,4 +1,13 @@
-class VaultLockedError(Exception):
+"""Compatibility layer for historic exception types."""
+
+from .core.errors import SeedPassError
+
+
+class VaultLockedError(SeedPassError):
     """Raised when an operation requires an unlocked vault."""
 
-    pass
+    def __init__(self, message: str = "Vault is locked") -> None:
+        super().__init__(message)
+
+
+__all__ = ["VaultLockedError", "SeedPassError"]