[BUG] Task-list checkboxes render as literal [ ] / [x] inside markdown tables in the desktop app's file viewer

## Summary

In the Claude desktop app's file viewer (Code tab), GitHub-flavored task-list checkboxes render as
interactive checkboxes in normal list context, but render as literal `[ ]` / `[x]` text when they
appear inside a markdown table cell. GitHub itself renders both.

This matters for progress/plan files, where a per-row status column is the natural layout: a table
of repositories × hosts with a checkbox per cell is unreadable in the viewer and has to be rewritten
as a flat list to be usable.

## Environment

- Claude desktop app 1.52386.6, Code tab, built-in file viewer
- Claude Code 2.1.269
- macOS 26.6.2 (Apple Silicon)

## Repro

Save as `repro.md` and open it in the desktop app's viewer:

```markdown
# Checkbox rendering

## In a list — renders as checkboxes

- [x] done item
- [ ] open item

## In a table — renders as literal text

| Repo | macOS | Linux | Windows |
|---|---|---|---|
| alpha | [x] | [x] | [ ] |
| beta | [x] | [ ] | [ ] |
```

**Expected:** the table cells show the same checkbox glyphs as the list above, as they do on GitHub.

**Actual:** the list renders checkboxes; the table cells show the raw characters `[x]` and `[ ]`.

## Notes

- Not a blocker — the workaround is to flatten the table into a list, which is what I did.
- GFM's spec technically only defines task list items as list items, so rendering them in tables is
an extension; GitHub, and several other renderers, support it. If matching GitHub is not intended
here, this is a feature request rather than a bug, and can be relabelled.

Start by opening the provided repro.md in the Claude desktop app's Code-tab file viewer and compare task-list rendering in the list and table contexts. Determine whether the viewer is intended to match GitHub's table-cell behavior; done means the expected behavior is decided and, if supported, table cells display checkbox glyphs rather than literal [x] and [ ].

Written by the indexing model from the issue text.