Show IC subcircuit preview on hover

[darktorres]

Description

Show a floating preview of an IC's internal circuit when the user hovers over it, so users can see what's inside without double-clicking.

Implementation Guide

1. Generate preview image

• Render the IC's internal circuit to a QPixmap at reduced scale using QGraphicsScene::render()
• Cache on the IC element, invalidate when source changes

2. Show on hover

• Override hoverEnterEvent() in IC to show a custom frameless popup widget
• Dismiss on hoverLeaveEvent() with a short delay (300ms)
• Limit preview resolution (max 300x200) and skip for very large circuits

Key files

• App/Element/IC.h/.cpp — hover events, preview generation
• App/Element/ICRegistry.h/.cpp — blob access for embedded ICs