Support multiple agents per-repo override

[Binlogo]

As mentioned in the document:

The same agent is used everywhere (no per-repo/worktree overrides, no environment variable overrides).

I'm not sure if this is just a statement or an intentional design goal.

For some reason, I suggest updating to support per-repo overrides:

• Different agents function slightly differently depending on the project type.
• Due to agent usage limitations, users need multiple agents to balance token consumption.
  • Additionally, xlaude is excellent, and users want to use it consistently. 🥰

@Xuanwo, what do you think? If you agree, I'll work on it.

[Xuanwo]

I don't have such use case but it looks good to me, welcome to work on it!