This reverts commit 1b52da3587325715f06948d5d526f71b00c7d9fb.
The session parent-child tree display in sidebar is visually unappealing
and unnecessary. The branch button behavior during AI response is also
intentional - users should not switch branches mid-conversation.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>