[Feature]增加自定义模型选项

[sagezhj]

Problem Description
One of the primary needs when using a generic client is to have access to a custom model API (such as ollama). However, this custom model API includes many open-source models (like qwen and glm), which cannot be called via geekchat.

Proposed Solution
The solution could involve manually adding preset selectable models in the settings. This way, new chat options can include these models. Additionally, when starting a new chat, users can choose a custom model and directly input the model name into the list of preset selectable models.

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问题描述
使用通用客户端的一大需求就是拥有自建模型API（如ollama），而自建模型API里包含很多的开源模型（如qwen、glm），均无法通过geekchat调用。

解决思路
可以在设置中，手动增加预设可选模型，以供新对话时选择。同时可以在开启新对话时，选择自定义模型，直接输入模型名称，录入至预设可选模型。