Markdown tables in agent chat output render as literal pipe text, not HTML tables #44

Summary

Markdown tables in agent chat output are not rendered as HTML tables — they appear as literal pipe-delimited text (| # | Title | etc. with the |---| separator row shown verbatim).

This is a follow-up to #37 (render assistant text as Markdown). The Markdig pipeline added there only enables DisableHtml():

private static readonly MarkdownPipeline MarkdownPipeline = new MarkdownPipelineBuilder()
    .DisableHtml()
    .Build();

GitHub-Flavored Markdown pipe tables are a Markdig extension that is not enabled by default, so table syntax falls through as plain paragraphs.

Expected

A GFM table renders as an HTML <table> (with <thead>/<tbody>/<tr>/<th>/<td>).

Proposed change

Enable the pipe-tables extension on the pipeline in ChatOutputHtmlRenderer, e.g. .UsePipeTables() (or .UseAdvancedExtensions() if other GFM features such as task lists / autolinks are also wanted). Keep DisableHtml() so raw HTML is still suppressed.

Add .chat-text table / th / td CSS to chat-output-shell.html so the rendered table has borders and padding.

Affected files (expected)

• Phantom.Workspaces.Agent.Gui/ViewModels/DocumentModels/ChatOutputHtmlRenderer.cs — enable the table extension on the pipeline
• Phantom.Workspaces.Agent.Gui/Assets/chat-output-shell.html — table CSS
• Phantom.Workspaces.Agent.Gui.Tests/ChatOutputHtmlModelTests.cs — add a test asserting a pipe table renders to <table>/<th>/<td>