[Feature]: Native TodoWrite-like progress panel for multi-step agent tasks

## Summary

Add a native TodoWrite-like progress panel for multi-step agent tasks, so users can clearly see what the agent is doing and how far the task has progressed.

## Component(s) Affected

- [ ] Core / Backend (app, agents, config, providers, utils, local_models)
- [x] Console (frontend web UI)
- [ ] Channels (DingTalk, Feishu, QQ, Discord, iMessage, etc.)
- [x] Skills
- [ ] CLI
- [ ] Documentation (website)
- [ ] Tests
- [ ] CI/CD
- [ ] Scripts / Deploy

## Problem / Motivation

When an agent performs a long or multi-step task, the current UI mainly shows tool calls and assistant messages. It is hard for users to quickly understand:

- what steps the agent planned
- which step is currently running
- which steps are completed
- whether any step failed or was skipped

Some agent environments provide a side progress panel, similar to a TodoWrite task list. This makes long-running debugging, deployment, code review, and troubleshooting tasks much easier to follow.

Currently, the agent can manually output a Markdown checklist, but that is only a normal message and not a persistent progress UI.

## Proposed Solution

Add a native todo/progress mechanism for agents.

For example, provide a built-in tool or event API such as:

```text
TodoWrite