GHSA-fmqh-xp37-5hr8: Open WebUI: Channel members can overwrite another member's message via the chat completions endpoint

In Open WebUI (a chat interface tool), any member with permission to post in a channel could edit and rewrite messages from other members while keeping the original author's name attached. This happened because the chat completions endpoint (the part of the software that handles message edits) only checked if the person had write access to the channel, but never verified they actually wrote the message being edited. A separate message editing route had the correct check, so the two code paths disagreed about who could modify messages.