refactor: add String() methods to domain types, replace string() casts

internal/domain/types.go

@@ -6,11 +6,20 @@ package domain
 // ImageID is a Docker image identifier (ID or tag).
 type ImageID string
 
+// String implements the fmt.Stringer interface.
+func (id ImageID) String() string { return string(id) }
+
 // ContainerID is a Docker container identifier.
 type ContainerID string
 
+// String implements the fmt.Stringer interface.
+func (id ContainerID) String() string { return string(id) }
+
 // UnparsedURL is a URL stored as a plain string without parsing.
 // Use this instead of string when the value is known to be a URL
 // but should not be parsed into a net/url.URL (e.g. webhook URLs,
 // compare URLs from external payloads).
 type UnparsedURL string
+
+// String implements the fmt.Stringer interface.
+func (u UnparsedURL) String() string { return string(u) }