Add panel tree view with layout preservation fixes

[fgodoy]

Summary

This PR adds a toggleable panel tree view and includes the follow-up layout fixes needed to keep the panel geometry consistent.

Changes

• add a toggleable tree view inside the file panel
• integrate the tree view into panel layout, menu and resources
• keep the panel info line below panel 1 content instead of under the tree area
• preserve the visible left/right panel proportion when toggling the tree with Ctrl+Shift+T
• add .gitignore entries for local build output generated during development

Validation

• build passed in Debug|Win32
• build passed in Release|Win32
• build passed in Release|x64
• manual smoke test confirmed the tree toggle and layout behavior

Personal Note

I have been a big fan of Servant Salamander and have been using it since the late 1990s. I even own a license.

I have always missed having a tree view in the panels, so I am very happy to be able to contribute this functionality back to the project.

[KRtekTM]

This is great. I integrated the feature into the Samandarin fork v0.2, just keyboard shortcut was changed to ctrl+shift+y (because ctrl+shift+t was already used for new tab in left panel).

[fgodoy]

Nice! Really happy to see it integrated into the Samandarin fork v0.2!!
Ctrl+Shift+Y sounds like a smart choice since Ctrl+Shift+T was already taken. Thanks for the integration and adjustment!