fix: open help dialog with tui/open-help in SDK

[AksharP5]

What does this PR do?

• Allows /tui/open-help to open the help command dialog in the TUI.
• The endpoint previously returned success without triggering any UI action. Publishing the same TUI command used by /help opens the help dialog as expected.

How did you verify your code works?

• bun dev -- --port 4096 (Should open OpenCode)
• curl -X POST http://127.0.0.1:4096/tui/open-help (in different terminal/window)
• Go to terminal where you ran bun dev, help dialog should show up now

Issue

• Closes /tui/open-help returns success but does nothing #8595

Screenshots/Videos

Before:

tui-open-help-dev.mov

After:

tui-open-help-feature.mov

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found