Fix Velocity 4 injection and add backend startup notifications

[iareanthony]

AI assistance disclosure

Codex was used to assist with diagnosing the Velocity 4 compatibility issue, preparing the code changes, and refining the implementation. The resulting changes were reviewed, tested, and validated by the contributor before submission.

Summary

This change fixes PlayerLifecycleListener initialization under Velocity 4 and adds player-facing title notifications while managed backend servers start.

Changes

• Replace javax.inject.Inject with com.google.inject.Inject
• Show a title while an offline managed server is starting
• Show a title when the server is ready and transfer is beginning
• Show a failure title if startup or readiness checks fail
• Preserve existing connection, timeout, fallback, and shutdown behavior
• Preserve the existing unit-test expectations by using titles rather than additional chat messages

Root cause

Under Velocity 4, Guice did not recognize the listener constructor annotated with javax.inject.Inject, causing Impulse initialization to fail with:

[Guice/MissingConstructor]: No injectable constructor for type PlayerLifecycleListener