fix: handle mentions when resending message

[EurFelux]

What this PR does

修改了重传消息时对用户消息中的mentions的处理逻辑。原本只有在不含关联助手消息时才会处理mentions，因此会出现当不含关联助手消息时连续两次重传会使用不同模型的诡异情况。

现在，重传消息会根据mentions和已有的关联助手消息中使用的模型来判断是否应该创建新消息。已存在的助手消息总是会根据其原有模型进行重传，而存在于mentions却不存在于关联助手消息的模型会创建新消息。

Fixes #7816

Why we need it and why it was done in this way

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The following alternatives were considered:

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Breaking changes

If this PR introduces breaking changes, please describe the changes and the impact on users.

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Release note

[Copilot]

Pull Request Overview

This PR fixes message resending logic when user messages contain model mentions. Previously, mentions were only processed when no associated assistant messages existed, causing inconsistent behavior during consecutive resends. The new logic properly handles mentions by comparing them with existing assistant message models and creates new messages only for models mentioned but not already present.

• Separates the handling of existing assistant message resets from new mention-based message creation
• Adds logic to compare mentioned models with existing assistant message models
• Creates new assistant messages only for models that are mentioned but not already present

Comments suppressed due to low confidence (1)

src/renderer/src/store/thunk/messageThunk.ts:1180

• [nitpick] The variable name 'originModelSet' should be renamed to 'existingModelSet' or 'currentModelSet' for better clarity about what it represents.

      const originModelSet = new Set(assistantMessagesToReset.map((m) => m.model).filter((m) => m !== undefined))

[0xfullex]

@MyPrototypeWhat 要是没问题review approve一下哈

[MyPrototypeWhat]

@MyPrototypeWhat 要是没问题review approve一下哈

还没来及测,我下午看下

[MyPrototypeWhat]

这个else应该可以跟上面合并

1. 有mentions优先按照mentions来
2. 没有则 ...(assistantMessagesToReset.length === 1 ? { model: assistant.model } : {}) 动态判断是助手model还是自身model

[EurFelux]

合并了，mentions在后面处理。

[MyPrototypeWhat]

LGTM