[FEATURE]: Expose question "ask" channel for SDK/plugins to use

[eXamadeus]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

As originally discussed in #6330 there was a desire to build a way for plugins and clients to "ask" questions. The request QuestionTool implemented that functionality in core and exposed most of the endpoints necessary for this system to work.

One significant endpoint that was not exposed was the /question/ask endpoint. The request is simple:

• Expose the Question.ask functionality via the server

This will allow both SDK users and plugin developers to use the new ask tool.

[!NOTE] This exposes the question.ask functionality for the SDK and API but the plugin is still stuck on v1 of the SDK. I have another PR to upgrade the plugin system to provide a v2 SDK client here: https://github.com/anomalyco/opencode/pull/8380

[github-actions[bot]]

This issue might be a duplicate of existing issues. Please check:

• #6330: [FEATURE]: Generic UI Intent Channel for cross-client plugin-driven UX — proposes a broader solution to expose question/UI functionality to plugins and SDKs across all clients (TUI, Desktop, Web)
• #7801: [FEATURE]: Plan Mode + Question tool can auto switch to Build mode — demonstrates need for Question tool functionality to work seamlessly with other features
• #8132: Question tool documented but not available in runtime — highlights that the Question tool isn't currently available in runtime, relevant to SDK/plugin exposure goals
• #7599: Question tool content missing in Web UI (opencode serve) — shows that Question tool UI rendering is incomplete across different clients

Feel free to ignore if none of these address your specific case.