Key Additions & Changes:
Interactive Length Control: Replaced the static "Length" text with an editable SliderControl component.
Vector Math Implementation: Added handleUpdateLength, a function that recalculates the wall's end position ($P_{end}$) based on the user's input while preserving the wall's original direction.
Real-time Geometry Updates: Integrated the change with useScene and dirtyNodes to ensure the 3D mesh updates instantly in the viewer as the slider moves.
UX Consistency: Used the existing SliderControl and PanelSection patterns to match the Pascal Editor's design system.
Fixes#191
