The tab context menu has "Copy Path", "Open in Terminal", and "Reveal In
Project Panel" but no way to reveal the file in the system file manager.
This action already exists in three other context menus (editor
right-click, project panel, outline panel) but was missing from tab
right-click.

## Changes

Adds a platform-specific entry to the tab context menu:
- **macOS:** "Reveal in Finder"
- **Windows:** "Reveal in File Explorer"
- **Linux:** "Reveal in File Manager"

Placed after "Copy Relative Path" and before "Pin Tab". Gated behind
`is_local` (including WSL with host interop) to match the project
panel's behavior. Uses the existing `project.reveal_path()`
infrastructure, which handles platform-specific file manager invocation
and WSL path conversion.

## Prior art

Every major editor has this in the tab context menu:
- VS Code: "Reveal in Finder" (macOS) / "Reveal in File Explorer"
(Windows)
- JetBrains IDEs: Right-click tab -> "Open in" -> "Finder"
- Sublime Text: Right-click tab -> "Reveal in Finder"

Zed already has this in the editor body right-click menu (`Cmd-K R`),
project panel (`Alt-Cmd-R`), and outline panel. The tab context menu was
the only place it was missing.

This contribution was developed with AI assistance (Claude Code).

Release Notes:

- Added "Reveal in Finder" to the tab context menu

## Screenshot

![Reveal in Finder in tab context
menu](https://github.com/mvanhorn/zed/releases/download/untagged-02ded227b30e3bcce8db/IMG_8537.png)

---------

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>