Picking vertex shader for lines.
Adds uNodeId uniform and vNodeId/vElementId outputs.
Strips colormap and color varyings (not needed for picking).
Mirrors the visual line shader's near-plane safety, max-pixel-width
clamp, and width/sharpness sanitization for pick/visual parity.
Picking vertex shader for lines. Adds uNodeId uniform and vNodeId/vElementId outputs. Strips colormap and color varyings (not needed for picking). Mirrors the visual line shader's near-plane safety, max-pixel-width clamp, and width/sharpness sanitization for pick/visual parity.