/experimental ask-user should render Markdown tables correctly

### Describe the feature or problem you'd like to solve

When /experimental ask-user returns content that includes a Markdown table, the table does not render correctly in the terminal UI. This makes structured comparisons hard to read and reduces the usefulness of ask_user for workflows where the user needs to choose between options, review tradeoffs, or inspect tabular data.

### Proposed solution

Render GitHub-flavored Markdown tables correctly in /experimental ask-user, with proper column alignment, borders or spacing, and wrapping behavior that remains readable in narrower terminal widths.

### Example prompts or workflows

_No response_

### Additional context

Expected behavior: tables should be readable and preserve row/column structure inside the /experimental ask-user flow.

Actual behavior: table formatting breaks, so columns collapse or become visually misaligned.

Start by locating the /experimental ask-user terminal UI entry point and its Markdown rendering path. Reproduce the issue with a GitHub-flavored Markdown table at narrow and normal terminal widths, then verify that columns remain aligned and readable while preserving row and column structure.

索引モデルが issue の本文から書いたものです。