[feature] Make workspace management discoverable from the sidebar

[zerob13]

Summary

Workspace lifecycle management exists in Settings, but it is difficult to discover from the sidebar where users interact with workspaces. The Settings navigation also places Environments under the Models group.

Priority: P2 UX

Current behavior

• Environment Settings supports active/archived views, reorder, open, default, archive, restore, and remove.
• The sidebar project-group menu primarily exposes order movement and Session creation behavior, but not a clear Open folder, Archive, or Manage workspaces path.
• src/shared/settingsNavigation.ts assigns settings-environments to groupKey: 'models' even though the route represents workspace/project setup.

Issue #1785 and PR #1787 implemented the underlying directory management contract. The remaining problem is entry-point discoverability, not missing persistence APIs.

Related contracts and documentation

• docs/features/complete-directory-management/spec.md is the maintained contract for archive/remove/reorder/default behavior and accessible move actions.
• docs/architecture/session-management.md assigns directory lifecycle to src/main/project/, separate from provider/model configuration.

The navigation hierarchy should reflect that ownership and let the sidebar delegate to the existing management surface.

Impact

• Users may assume archive/remove/default management does not exist.
• Workspace actions require leaving the primary context and knowing the exact Settings location.
• Placing Environments under Models creates a misleading product taxonomy.
• Missing-path and duplicate-name recovery are harder to reach.

Proposed experience

• Add a compact workspace context menu with safe shortcuts:
  • New chat in workspace
  • Open folder
  • Set as default
  • Archive
  • Manage workspaces
• Keep destructive removal and archived restoration in the full Settings surface with existing confirmation contracts.
• Move Environments to the Setup/general workspace group in Settings navigation.
• Ensure keyboard and screen-reader users can reach every action.

Acceptance criteria

• Every visible active workspace has an accessible management entry point.
• Open, default, archive, and manage actions delegate to existing typed Project APIs.
• Remove confirmation semantics remain unchanged and never delete filesystem data.
• Environments is no longer grouped under Models.
• Archived/missing/default states display only eligible actions.
• Renderer tests cover keyboard access, menu eligibility, navigation, and project snapshot refresh.

User benefit

Users can find and understand workspace management from the place where workspaces are used, without confusing it with model configuration.