Migrate backend to Vert.x 4 and JDK 17

[yunyu]

Summary

• upgrade the Maven build to target JDK 17 and use the Vert.x 4.5.9 stack with explicit Jackson dependencies
• adapt verticles and handlers to Vert.x 4 callback APIs while keeping the existing callback-driven flow for room management
• update the SockJS bridge and HTTP bootstrap logic for the Vert.x 4 web layer

Testing

• mvn -DskipTests package

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https://chatgpt.com/codex/tasks/task_e_68d41cab439483228df1c6e248c9aa85