fix: make workspace icons consistent between active and inactive states

[xielixing]

Problem

Fixes #1849

When a workspace is active, it showed a \DotMatrixArrowRightIcon\ (arrow) instead of the normal folder/letter icon. This made active and inactive workspaces look like different entity types rather than siblings.

Root Cause

In \WorkspaceItem.tsx, both the assistant workspace branch and the normal workspace branch used \isActive ?\ to conditionally render different icons:

• Active: arrow icon (\DotMatrixArrowRightIcon)
• Inactive: folder icon (\FolderOpen) or letter avatar

Fix

Remove the \isActive\ conditional from both branches so active and inactive workspaces always use the same icon:

• Assistant workspaces: always show the letter avatar
• Normal workspaces: always show \FolderOpen\

The active state is still visually indicated by the existing \is-active\ CSS class, \�ria-current, and \data-workspace-active\ attributes — only the icon swap was removed.

Changes

• \WorkspaceItem.tsx: Removed \DotMatrixArrowRightIcon\ import and the two \isActive ?\ icon conditionals
• \WorkspaceListSection.scss: Removed dead \workspace-item-active-icon\ and \�ssistant-item-active-icon\ CSS rules, and cleaned up hover selector that referenced \�ssistant-item-active-icon\
• \WorkspaceListSectionLayout.test.ts: Added test verifying source/stylesheet no longer contain \DotMatrixArrowRightIcon\ or \�ctive-icon\ classes

Testing

• Validated all assertions pass (no \DotMatrixArrowRightIcon\ or \�ctive-icon\ references remain in source or stylesheet)
• \isActive\ is still used elsewhere in the component for \is-active\ class, \�ria-current, \data-workspace-active, git info, and session logic — only the icon swap was removed
• \FolderOpen\ import was already present and remains used