[codex] Fix repeated TTS playback

[devashishmamgain]

Jira

• TDH-269

Summary

• Add a short-lived voice-output message tracker keyed by message key or timestamp fallback.
• Skip repeated TTS playback when the same incoming message is delivered multiple times.

Root Cause

Duplicate delivery of the same bot message could call the native speech synthesis path repeatedly, causing the same response to be spoken 3-4 times.

Validation

• node --check webplugin/js/app/media/media-service.js
• git diff --check