feat: cloud project rename, delete, and new-thread sidebar actions

[Mng-dev-ai]

Summary

• Cloud workspaces in the sidebar now render the same header actions as local ones: new thread, rename, and delete (previously read-only).
• Rename/delete proxy to the VPS via new useCloudUpdateWorkspaceMutation / useCloudDeleteWorkspaceMutation hooks and cloudChatService.updateWorkspace / deleteWorkspace.
• The workspace context menu and dropdown now track isCloud so rename/delete route to the correct backend; cloud and local IDs are UUIDs from separate DBs (no collisions).
• New-thread on a cloud project routes to the landing composer with the cloud target preselected and the run location flipped to cloud.
• LandingPage now consumes the sidebar new-thread target keyed on location.key (not the target ID), so re-clicking the same workspace re-applies its run location even after a manual toggle.
• SidebarChatGroup shell now owns the new-thread + context-menu header buttons for both local and cloud groups instead of taking them as a headerActions node.

Test plan

• Cloud project shows new thread, rename, and delete actions on hover
• Renaming a cloud project updates the VPS and refreshes the sidebar
• Deleting a cloud project removes it and its chats from the sidebar
• Clicking "new thread" on a cloud project opens the landing composer with that workspace preselected and run location set to cloud
• Local project rename/delete/new-thread still work unchanged
• Re-clicking the same cloud project's new thread after toggling run location re-applies cloud