`getChatSuggestions` previously picked the largest installed model by file
size, on the assumption that bigger models give better suggestions. This
is unsafe: if any installed model exceeds available VRAM (e.g.
llama3.1:405b on a 96 GB GPU), Ollama spends minutes trying to load it
and the request 500s — making the chat page unusable for anyone who
happens to keep a flagship-sized model on disk.
Chat suggestions are short prompts that don't benefit from a flagship
model anyway. Prefer the user's selected `chat.lastModel` when set, and
fall back to the smallest installed model otherwise. `OllamaService.getModels()`
already excludes embedders, so the fallback always picks a chat model.
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