feat: support arrow-directions in plantuml

[Chaaph]

Pull Request

Slice-level architecture rules: PlantUML diagram validation now also works with directional arrows.

Change Type

• Bug fix
• Feature
• Documentation
• Refactoring

[lukasniessen-bain]

Requesting one parser change before merge: the new re.sub runs across the entire line and accepts any lowercase word. That means a relationship such as [api-d->handler] -> [db] is rewritten with a different source name, while an unsupported token such as -banana-> is accepted as an arrow direction.

Please match/normalize the direction only within the relationship operator and restrict it to the intended PlantUML direction aliases. Please also assert the generated rule's source and target and add coverage for an endpoint containing direction-shaped text and for an unsupported token. The existing -d-> happy-path test is a useful starting point.