[Feature]: Add Remote environments filtering to desktop clients

Problem

The desktop clients on both Windows and macOS do not offer a way to filter the sidebar/projects by Remote environments. They can be filtered by Project only.

The mobile client already supports filtering by remote environment, so desktop and mobile experiences are inconsistent. This makes it difficult to locate and work with projects and threads when several remote environments are configured.

Requested behavior

Add a Remote environments filter to the Windows and macOS desktop clients, matching the mobile client capability as closely as practical.

The filter should let users:

• show all environments (default);
• select one or more remote environments; and
• limit the displayed projects/threads to those environments.

Expected outcome

A user with multiple remote environments can quickly focus the desktop UI on a chosen remote environment instead of manually scanning mixed local and remote projects or relying only on project filtering.

Notes

This request is specifically about parity with the existing mobile capability, rather than a general new filtering system. It may overlap with broader sidebar-filtering work such as #3523, but the missing Remote environments filter in both desktop clients is the concrete gap being reported.

Start by locating the existing mobile Remote environments filtering and the Windows and macOS desktop sidebar/project filtering entry points. Match the mobile behavior where practical, including the all-environments default, single or multiple environment selection, and filtering of displayed projects and threads; verify both desktop clients behave consistently.