[FEATURE] Desktop file panel: show hidden files, resolve symlinks, and handle binary files gracefully

The file panel in the Claude Code desktop app has three related gaps that make it hard to use with real-world project structures:

1. Hidden files and folders are not visible
Dot-prefixed files and directories (.claude/, .env, .env.local, etc.) are invisible in the sidebar. There is no toggle to show them. For users whose most important config files are hidden, this makes the panel mostly decorative.

Request: Add an opt-in toggle (e.g. "Show hidden files") to display dot-prefixed entries in the file tree.

2. Symlinks are not followed
Symlinked directories appear in the tree but cannot be navigated into. Clicking them does nothing or fails silently.

Request: Resolve and traverse symlinks in the file panel the same way a terminal or IDE would.

3. Binary files (images, PDFs) open as raw ASCII
Opening a PNG, JPEG, or PDF in the file panel renders garbage characters. There is no graceful fallback.

Request: Either render images inline, or show a clear "Binary file — cannot preview" message instead of raw bytes.

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Environment:

• Platform: macOS
• App: Claude Code Desktop