Sortable Spaces list in sidebar (alphabetical)

[madmoneymike5]

Summary

The Spaces (workspace) section at the top of the sidebar can only be ordered by manual mouse drag-reorder. A sort option — especially alphabetical — would be useful for users with many workspaces.

Current behavior

• Spaces render in manual order; reordering is drag-only (DragTarget::WorkspaceReorder).
• ui.agent_panel_sort (spaces/priority) applies to the Agents section only, not the Spaces list.
• ui.sidebar.spaces.rows controls row display tokens, not ordering.
• New workspaces are appended without a stable alphabetical position, so a hand-sorted list drifts over time.

Requested behavior

A config option to sort the Spaces list, e.g.:

[ui.sidebar]
spaces_sort = none | alpha | manual   # manual = current drag order

• alpha: sort top-level Spaces by displayed name (case-insensitive), preserving worktree parent/child grouping and indentation.
• manual (default): current behavior, drag-to-reorder.

Why

With 8+ workspaces, keeping the list alphabetical by dragging is fragile: every new workspace re-burrows the order. Alphabetical (or at least pin-to-top) would keep the sidebar stable.

(filed as issue #3543, closed as discussion-welcome — moving here)