docs: clarify Unreal connection ticking

[clockwork-labs-bot]

Summary

• update the shared connection docs to say Unreal clients can either call FrameTick() or enable SetAutoTicking(true)
• replace the Unreal reference claim that messages are processed automatically with the actual queued-message/tick behavior
• document FrameTick and SetAutoTicking in the Unreal client reference

Validation

• corepack pnpm build from docs/