Snap overlay when dragging the launcher (center + default position) #659

When dragging the SuperCmd launcher to reposition it, show a Raycast-style overlay with snap targets for:

• screen center
• the default / reset position (top-center)

Dropping near a target should snap there. Dropping elsewhere should keep the custom position (already remembered across restarts). Reset Launcher Position should still work.

Why

Dragging works, but without guides it is hard to hit center or the default spot exactly.

Current behavior

The panel can be dragged and the position is persisted. Reset Launcher Position exists (see #213 / PR #218). There are no visual snap guides while dragging.

Suggested behavior

1. Start a drag on the launcher panel.
2. Show faint overlay marks for center and default position.
3. Magnetic snap when close to a mark.
4. Overlay disappears on mouse-up.

Related: #213 covered persist + reset. This request is only the visual snap overlay on top of that