1. ParticipantForm: set branch_id from session in mount() so new
   participants get the active branch (was null, invisible in list)
2. SpaceLayoutService::update: compare config BEFORE updating the model
   so change detection works (was comparing same value to itself)
3. ReceiptSettings: use session branch_id instead of user->branch_id
   which could be null, preventing template save
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>