Folders now list alphabetically (case-insensitive) everywhere they're
shown — sidebar, advanced conversation list, and the "Move to Folder"
menu — rather than creation order. listFolders() does the sort at the
DB layer; in-memory folder arrays are re-sorted after local
create/rename so newly added or renamed folders don't fall out of
order until the next reload.
Combine Conversations' AI-Assisted Merge no longer silently assumes
settings.defaultModel — added a model picker (reusing ModelSelectorView,
defaulting to the current default model/provider) so users can pick
which model performs the merge per-combine. ConversationMergeService.merge
takes optional mergeModelId/mergeProvider overrides.