webui : missing messages in latest branch of a conversation

[ggerganov]

The messages in the latest branch of a conversation disappear after switching to an older branch.

Repro:

Screen.Recording.2025-10-03.at.11.20.48.mov

[allozaur]

Fixing it right away. After refresh all the messages are shown, so this is some bug with how the store is working after regeneration.

[allozaur]

@ggerganov please test the #16408 and let me know if the issue is gone on your end