Add Edit Mode button to Sources sidebar for drag-reorder (hide drag handles when not editing)

[Yeraze]

Description

The Sources sidebar currently shows drag handles at all times, consuming visible screen real estate even when the user has no intention of reordering sources. A dedicated Edit Mode button would improve the UX by hiding drag handles by default and only revealing them when the user explicitly wants to reorder.

Proposed Behavior

• Add an Edit button next to the existing +Add button in the Sources sidebar header
• When Edit mode is inactive (default): drag handles are hidden; sources are not draggable
• When Edit mode is active: drag handles appear and sources can be reordered via drag-and-drop
• The Edit button (and drag reorder capability) should only be visible to users with appropriate admin/editor permissions

Why

• Drag handles clutter the sidebar and are rarely needed
• Permission-gating prevents unauthorized reordering in shared/multi-user deployments
• Consistent with common "edit mode" UX patterns (e.g. mobile app reordering)

Authored by NodeZero 0️⃣