refactor: remove internal/domain package, move types to correct packages

- ImageID + ContainerID → internal/docker/types.go
- UnparsedURL → internal/service/webhook/types.go
- Delete internal/domain/ entirely
- Update all imports throughout the codebase

internal/docker/types.go

@@ -0,0 +1,13 @@
+package docker
+
+// 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) }