add sidebar environment visibility toggles

[tarik02]

What Changed

• Add an environments dropdown to the sidebar project toolbar.
• Persist hidden sidebar environments as sidebarEnvironmentHiddenById.
• Filter sidebar projects and threads by visible environments.
• Keep at least one environment visible and hide the control when only one environment is configured.

Why

Users with many configured environments can keep the sidebar focused without disconnecting environments.

UI Changes

Not captured.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes