CV-QKD Security Map: Phase-Space Constellation & Key-Rate Grid

This is a 2D-native companion to the 3D continuous-variable QKD flythrough. Instead of flying a camera between two rendered planes, it draws the same GG02 protocol as two flat diagrams computed straight from the channel equations: a live quadrature scatter plot overlaying Alice's tight modulation cluster with Bob's noisier, loss-widened constellation, and a secret-key-rate heat map swept independently across fiber length and excess noise for the current modulation variance. The heat map exposes an algebraic fact the pulse animation never shows on its own — the security boundary sits at a fixed 3 dB loss threshold (T = 0.5) regardless of excess noise, because both Bob's mutual information and Eve's Holevo bound share the same noise denominator.