feat(desktop): Add file explorer sidebar and integrated code editor

[cristian1991]

Description

The desktop app currently lacks a way to browse and edit project files directly. Users need to switch to external editors to view or modify files referenced in conversations.

Proposed Solution

Add a resizable file explorer sidebar and tabbed Monaco editor to the desktop app:

• File Explorer: Tree view with expand/collapse, file type icons, refresh functionality
• Code Editor: Monaco-based editor with syntax highlighting for 100+ languages
• Tab Management: Multiple open files, modified indicators, close buttons
• File Watching: Detect external changes and prompt to reload
• Keyboard Shortcuts: Ctrl+S to save, Ctrl+W to close tab

Use Cases

• View files that Claude references in conversations without leaving the app
• Make quick edits to code files directly in the app
• Browse project structure while working with Claude

Additional Context

The editor integrates with the existing session workflow. The explorer panel can be toggled on/off via settings. Web platform gets graceful fallbacks (features disabled).

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• feat(app): Add file tree panel to session view #10239: feat(app): Add file tree panel to session view - This appears to be the same file explorer sidebar feature with a file tree panel for browsing and navigating project files

Feel free to ignore if this doesn't address your specific case.

[R44VC0RP]

Thanks for the detailed feature request, @cristian1991!

The file explorer sidebar portion is a duplicate of #10239, which has an active PR (#10236) in progress implementing the file tree panel with lazy-loading, persistent state, and file watcher integration.

The Monaco code editor integration is new scope not covered by #10239 - that could be a nice follow-up feature.

Closing as duplicate of #10239. Once PR #10236 merges, feel free to open a follow-up for the Monaco editor piece!

[cristian1991]

Just linking my PR #10299 here for visibility - it was submitted before this issue was created but I forgot to reference it.

It takes a different approach with a full Monaco editor and file operations (new/rename/delete/copy). Happy to adapt it to work alongside #10236 if there's interest.