Constructor Injection

The constructor injection initiative refactored high-value classes from the service locator pattern (calling `engine.getManager()` internally) to accepting dependencies via constructor parameters.

Motivation

The service locator pattern made unit testing difficult — tests had to create a full WikiEngine even when only one manager was needed. Constructor injection allows tests to pass lightweight stubs directly.

Classes Refactored

Seven high-value classes were converted, including core rendering and reference management components. Each class gained a constructor accepting its dependencies while maintaining backwards compatibility through a default constructor that falls back to service location.

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