[FEATURE] Add ability to resume from other session despite current ongoing session

## Feature Description

Right now, you can resume from a previous session when Claude Code hasn't yet been toggled on yet. However, if I want to potentially switch to another Claude Code session while you've already toggled it, then you need to 1) go to the current Claude Code session, 2) terminate the session, and 3) trigger `:ClaudeCode --resume`.

Ideally, we can just trigger something like `:ClaudeCode --resume` and that would just pull up the list of previous Claude Code session.

## Use Case

This would make Claude Code session management much easier.

## Proposed Solution

A nice solution would be to add a more generic `:ClaudeCodeCommand` that allows users to send arbitrary Claude Code commands, e.g. `:ClaudeCodeCommand clear` would run `/clear` within the Claude Code session.

## Alternatives Considered

The alternative is to 1) go to the current Claude Code session, 2) terminate the session, and 3) trigger `:ClaudeCode --resume`.

## Additional Context

首先追踪 `:ClaudeCode --resume` 的实现，以及活动中的 Claude Code 会话是如何管理的。将当前的恢复流程与提议的 `:ClaudeCodeCommand` 行为进行比较，然后确定预期的命令语义和会话切换边界。当恢复命令无需手动终止当前会话即可显示以前的会话，并且相关行为已通过测试覆盖（如果项目提供测试）时，即视为完成。

由索引模型根据 Issue 内容生成。