docs: add troubleshooting for Ollama memory errors (#11864)

* docs: add troubleshooting for "model requires more system memory" in Ollama

Add guidance for users encountering memory errors when using Ollama models
with Continue. Continue's higher default context length can trigger this
error even when models work in other tools. Documents the fix of reducing
contextLength in config, with examples for both YAML and JSON formats.

Ref: https://github.com/continuedev/continue/issues/11715

* docs: make ollama memory troubleshooting more concise

* docs: remove discussion link from ollama troubleshooting

* docs: fix broken link to ollama troubleshooting section