[BUG] Side-panel file viewer: <a> links are almost entirely non-interactive — no target info, no context menu, wrong click behavior

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

Description:

When viewing a Markdown file with links (both file links and intra-document anchors) in Claude Code's side panel, the link handling is broken in several distinct ways:

Clicking a link to a binary file (e.g. .xlsx, .pptx) silently opens the containing folder instead of the file — no error message, no fallback behavior, just silently the wrong outcome. A user has no way to tell the click "worked" versus silently failed.
Right-clicking a link shows no link-specific context menu at all. The context menu is identical to right-clicking anywhere else in the document — the only available option is "copy path" for the currently displayed file, not the link target. There is no "copy link", "open link", "open link in new tab," etc.
No hover affordance whatsoever. Hovering over a link produces no visual change, no tooltip, no status-bar preview of the target — standard browser behavior since the 1990s. There is no way to see where a link points before clicking it.
The link target is effectively unknowable through the UI. Combined with points 2 and 3, there is no way — hover, right-click, or otherwise — to inspect what a given link actually points to without blindly clicking it and observing the (possibly wrong, per point 1) result.
Intra-document links (e.g. a Markdown Table of Contents linking to #heading-anchors within the same file) don't work at all. Clicking a TOC entry does nothing — no scroll, no navigation to the target heading.

Impact: For a panel that renders and is described as a browser/viewer, elements are essentially non-functional as links — no target visibility, no standard interaction affordances, at least one confirmed wrong-behavior case for external file links (point 1), and a complete failure case for internal same-document navigation (point 5).

_No response_

The payload names no repository files or tests; start by reproducing the Markdown link cases in the Claude Code side-panel file viewer on macOS. Check file links, right-click and hover behavior, binary targets, and same-document anchors. Done means links expose their targets, provide appropriate actions, handle unsupported files clearly, and scroll to internal headings.

索引モデルが issue の本文から書いたものです。