Restore Agent V2 support in Chatflow

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### 1. Is this request related to a challenge you're experiencing? Tell me about your story.

We use Chatflow for multi-turn applications and need the capabilities provided by Agent V2 inside a Chatflow.

Agent V2 could be selected in Chatflow in Dify 1.16.0. Starting with 1.16.1, it was intentionally hidden from Chatflow by PR #39439 / commit `625ed2a0e7` (`fix(workflow): hide Agent V2 in chatflow`). The current frontend logic still enables Agent V2 only when the application is not in chat mode:

```ts
const shouldUseAgentV2 = agentV2Enabled && !isChatMode
```

As a result, Chatflow users can only use the legacy Agent node even when Agent V2 is enabled. This prevents us from using the new Agent implementation in a conversational, multi-turn flow.

Could the maintainers clarify whether restoring Agent V2 support in Chatflow is planned? If so, is there a target version, roadmap item, or tracking issue that users can follow?

### 2. Additional context or comments

- Agent V2 was hidden from Chatflow in PR #39439: https://github.com/langgenius/dify/pull/39439
- A related but different issue, #39161, concerns deployment of the Agent backend service rather than the plan to restore Chatflow support: https://github.com/langgenius/dify/issues/39161
- The Agent V2 workflow backend remains present, so this request is specifically about official Chatflow support and its expected timeline.

### 3. Can you help us with this feature?

- [ ] I am interested in contributing to this feature.

Start by reviewing PR #39439 and commit 625ed2a0e, then trace the frontend condition `agentV2Enabled && !isChatMode` and confirm how Chatflow selects its Agent implementation. Check the existing Agent V2 workflow backend and related issue #39161. Done requires a maintainer-defined restoration plan, implementation scope, and target version or tracking issue.

Written by the indexing model from the issue text.