Models now load live from every provider - no more dead or outdated model lists.

- Refresh model list works for every provider, cloud and local, and refreshes itself weekly
- Models are verified when you pick one: anything your key cannot use is removed, with the provider's own reason
- New model picker with search and tags: tested with your key / accepts images / free
- Image attachments work on more providers, and no longer need a caption
- Fixed Anthropic (Claude) chats failing completely
- Default Arabic dialect is now Modern Standard Arabic
